链表面试笔试题目总结

链表是最基本的数据结构，凡是学计算机的必须的掌握的，在面试的时候经常被问到，关于链表的实现，百度一下就知道了。在此可以讨论一下与链表相关的练习题。

1、在单链表上插入一个元素，要求时间复杂度为O(1)

解答：一般情况在链表中插入一元素是在末尾插入的，这样需要从头遍历一次链表，找到末尾，时间为O(n)。要在O(1)时间插入一个新节点，可以考虑每次在头节点后面插入，即每次插入的节点成为链表的第一个节点。

2、给定一个链表，判断是否有环。

解答：这个是一个经典的问题了，思路也很简单，我们首先设置两个指针p1，p2同时指向链表的头部，然后p1每次向后走1步，p2每次向后走2步。如果有环，那么有一步会出现p1=p2，如果p2已经到达了尾结点，则无环。复杂度：时间：O(n)，空间：O(1)

扩展：给定一个链表，找出环的入口位置。思路也是一样，用p1,p2指针。只是需要多做一步，那就是当p1=p2的时候，将p1重新指向链表的头结点，然后p1和p2都每次向后走一步，下一次p1=p2的结点就是环的入口。复杂度：时间：O(n)，空间：O(1)

3、遍历单链表一次，找出链表中间节点

解答：定义两个指针p和q，初始都指向链表头节点。然后开始向后遍历，p每次移动2步，q移动一步，当p到达末尾的时候，p正好到达了中间位置。

4、单链表逆置，不允许额外分配存储空间，不允许递归，可以使用临时变量，执行时间为O(n)

解答：这个题目在面试笔试中经常碰到，基本思想上将指针逆置。如下图所示：

实现：

Node* reverse_list(Node *head){Node *cur=head;Node *pre = NULL;Node *post = cur->next;
<span class="hljs-comment" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: italic; font-family: inherit; vertical-align: baseline; color: rgb(64, 128, 128); background: transparent;">//    Node *reverse_head = cur;</span><span class="hljs-keyword" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(149, 65, 33); background: transparent;">while</span>(post){cur->next = pre;pre = cur;cur = post;post = post->next;}cur->next = pre;
<span class="hljs-comment" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: italic; font-family: inherit; vertical-align: baseline; color: rgb(64, 128, 128); background: transparent;">//    reverse_head = cur;</span><span class="hljs-keyword" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(149, 65, 33); background: transparent;">return</span> cur;
}

扩展：链表翻转。给出一个链表和一个数k，比如，链表为1→2→3→4→5→6，k=2，则翻转后2→1→6→5→4→3，若k=3，翻转后3→2→1→6→5→4，若k=4，翻转后4→3→2→1→6→5，用程序实现。

实质是也是逆置，只不过是两个链表逆置后再串联起来。实现如下：

<span class="hljs-function" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; background: transparent;"><span class="hljs-keyword" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(149, 65, 33); background: transparent;">bool</span> <span class="hljs-title" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(25, 70, 157); background: transparent;">rotate_list</span><span class="hljs-params" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(0, 0, 255); background: transparent;">(Node *head,<span class="hljs-keyword" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(149, 65, 33); background: transparent;">int</span> k,Node* &newhead)</span></span>{<span class="hljs-keyword" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(149, 65, 33); background: transparent;">if</span>(k < <span class="hljs-number" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(64, 160, 112); background: transparent;">0</span>)<span class="hljs-keyword" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(149, 65, 33); background: transparent;">return</span> <span class="hljs-keyword" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(149, 65, 33); background: transparent;">false</span>;<span class="hljs-function" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; background: transparent;"><span class="hljs-keyword" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(149, 65, 33); background: transparent;">else</span> <span class="hljs-title" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(25, 70, 157); background: transparent;">if</span><span class="hljs-params" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(0, 0, 255); background: transparent;">(0 == k)</span>return <span class="hljs-keyword" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(149, 65, 33); background: transparent;">true</span></span>;<span class="hljs-keyword" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(149, 65, 33); background: transparent;">int</span> len = <span class="hljs-number" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(64, 160, 112); background: transparent;">0</span>;Node *node=head;<span class="hljs-keyword" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(149, 65, 33); background: transparent;">while</span>(node){++len;node = node->next;}<span class="hljs-keyword" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(149, 65, 33); background: transparent;">if</span>(k > len)<span class="hljs-keyword" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(149, 65, 33); background: transparent;">return</span> <span class="hljs-keyword" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(149, 65, 33); background: transparent;">false</span>;Node *one_end,*two_start;node = head;Node *post = node->next;<span class="hljs-keyword" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(149, 65, 33); background: transparent;">int</span> n=k;<span class="hljs-keyword" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(149, 65, 33); background: transparent;">if</span>(<span class="hljs-number" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(64, 160, 112); background: transparent;">1</span> == n){}<span class="hljs-keyword" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(149, 65, 33); background: transparent;">else</span>{<span class="hljs-keyword" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(149, 65, 33); background: transparent;">while</span>(n > <span class="hljs-number" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(64, 160, 112); background: transparent;">1</span>){<span class="hljs-comment" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: italic; font-family: inherit; vertical-align: baseline; color: rgb(64, 128, 128); background: transparent;">// rotate sublist one</span>node->next = post->next;post->next = head;head = post;post = node->next;--n;}}<span class="hljs-keyword" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(149, 65, 33); background: transparent;">if</span>(len-k <= <span class="hljs-number" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(64, 160, 112); background: transparent;">1</span>){ <span class="hljs-comment" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: italic; font-family: inherit; vertical-align: baseline; color: rgb(64, 128, 128); background: transparent;">// rotate sublist two</span>}<span class="hljs-keyword" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(149, 65, 33); background: transparent;">else</span>{one_end = node;node = post;post = post->next;two_start = node;n = len-k;<span class="hljs-keyword" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(149, 65, 33); background: transparent;">while</span>(n><span class="hljs-number" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(64, 160, 112); background: transparent;">1</span>){one_end->next = post;node->next = post->next;post->next = two_start;two_start = post;post = node->next;--n;}}newhead = head;<span class="hljs-keyword" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(149, 65, 33); background: transparent;">return</span> <span class="hljs-keyword" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(149, 65, 33); background: transparent;">true</span>;
}

5、用一个单链表L实现一个栈，要求push和pop的操作时间为O(1)

解答：根据栈中元素先进后出的特点，可以在链表的头部进行插入和删除操作

6、用一个单链表L实现一个队列，要求enqueue和dequeue的操作时间为O(1)

解答：队列中的元素是先进先出，在单链表结构中增加一个尾指针，数据从尾部入队，从头

部入队。

7、给定两个链表（无环），判断是否有相交。

解答：首先明确一点，如果两个链表相交，那么从第一个交点开始到尾结点结束，所有的结点都是公共结点。所以，两个有公共结点而部分重合的链表，拓扑形状看起来像一个Y，而不可能像X。

这也就是说，如果两个链表相交，那么这两个链表的尾结点肯定是公共结点，如果尾结点不是公共结点，那么这两个链表肯定不相交。

所以我们可以如下操作：依次遍历两个链表，最后判断尾结点是否相同，如果相同，则相交，如果不相同，则不相交。复杂度：时间：O(m+n)，空间：O(1)

或者一个链表的头结点指向另一个链表的尾节点，判断是否有环。

8、给定两个链表（无环），找到第一个公共节点。

解答：我们最容易想到的是从尾结点开始挨个向前比较，最后一个相同的就是第一个公共结点。（从后往前遍历）

但是单链表只能从前往后进行遍历，如果想要从后往前的话则需要先从前向后遍历一次，同时用栈来记录每一个结点，最后出栈，然后挨个对比，这样的确可行，但是却要额外付出O(m+n)的空间，时间复杂度O(mn)。（单链表+栈）

仔细想想，我们可以先分别遍历两个单链表，记录长度m和n（无妨假设m>n），然后先让长度为m的链表向后走(m-n)步，接着两个链表同时向后遍历，第一个相同的结点就是要求的第一个公共结点。复杂度：O(m+n)m,n分别为两个链表的长度；空间：O(1)

PS：另外还有一种巧妙的方法是把在一个链表尾部插入另一个链表，然后判断合成的新链表是否有环。环入口即为第一个公共点。

可参考：http://www.voidcn.com/blog/wcyoot/article/p-2762597.html

扩展：两个链表，找出他们的第一个交点，要求每个链表只能遍历一次，可以对链表进行任何操作，空间O(1).

题目告诉说可以对链表进行任何操作，这是一个没有用到的条件（大家一定要注意到题目中没有用到的条件，往往是解题的关键所在）。

1.遍历第一个链表List1，将每一个节点的next都置为NULL。

2.遍历第二个链表List2，List2的尾节点就是第一个交点。

9、给定2个链表，求这2个链表的并集(链表)和交集(链表)。不要求并集(链表)和交集(链表)中的元素有序。输入：List1:10->15->4->20，List2:8->4->2->10输出：交集(链表)：4->10；并集(链表)：2->8->20->4->15->10

法一：简单直观的方法：

InterSection(list1,list2):初始化结果链表为空，遍历链表1，在链表2中查找它的每一元素，如果链表2中也有这个元素，则将该元素插入到结果链表中。

Union(list1,list2): 初始化结果链表为空，将链表1中的所有元素都插入到结果链表中。遍历链表2，如果结果链表中没有该元素，则插入，否则跳过该元素。

法二：可适应归并排序，not clear。

法三：Hash法

Union(list1,list2)，首先用链表1初始化结果链表，创建一个空的hash表。遍历链表1，将链表中的元素插入到hash表。然后遍历list2，对于list2中的元素，如果hash表中不存在该元素，则同时将该元素插入到结果链表中，如果hash表中已经存在，则忽略该元素，继续遍历下一个元素。

InterSection(list1,list2)，首先初始化结果链表为NULL，创建一个空的hash表。遍历list1，将list1中的每一个元素都插入到hash表中。然后遍历list2，对于list2中的元素，如果已经存在于hash表中，则将该元素插入到结果链表，如果不存在与hash表中，则忽略该元素，继续遍历下一个元素。

参考：http://blog.csdn.net/lalor/article/details/7430631

10、从单链表返回倒数第n个元素

普通，基本思路就是用栈，一一压栈，再弹栈，第n个元素就可出来。

进阶，看到栈，就应该想到递归，递归是天然的栈。用全局变量，实现如下：

Node* pn_elem = NULL;
<span class="hljs-keyword" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(149, 65, 33); background: transparent;">int</span> nn;
<span class="hljs-function" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; background: transparent;"><span class="hljs-keyword" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(149, 65, 33); background: transparent;">void</span> <span class="hljs-title" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(25, 70, 157); background: transparent;">recursive</span><span class="hljs-params" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(0, 0, 255); background: transparent;">(Node* node)</span></span>{<span class="hljs-keyword" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(149, 65, 33); background: transparent;">if</span>(!node)   <span class="hljs-keyword" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(149, 65, 33); background: transparent;">return</span> ;recursive(node->next);<span class="hljs-keyword" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(149, 65, 33); background: transparent;">if</span>(<span class="hljs-number" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(64, 160, 112); background: transparent;">1</span>==nn)   pn_elem =  node;--nn;
}

高级，维护两个指针，两个指针相差n个元素，当前面的指针到达链表末尾，后面指针所指的元素即是所求的元素。实现如下

Node* last_n_elem(Node*node,<span class="hljs-keyword" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(149, 65, 33); background: transparent;">int</span> n){<span class="hljs-keyword" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(149, 65, 33); background: transparent;">if</span>(node! || n<<span class="hljs-number" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(64, 160, 112); background: transparent;">1</span>)    returnNULL;Node *p=node,*q=node;<span class="hljs-keyword" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(149, 65, 33); background: transparent;">while</span>(n><span class="hljs-number" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(64, 160, 112); background: transparent;">0</span> && q){q=q->next;--n;}<span class="hljs-keyword" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(149, 65, 33); background: transparent;">while</span>(q){q=q->next;p=p->next;}<span class="hljs-keyword" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(149, 65, 33); background: transparent;">return</span> p;
}

11、链表元素去重，从未排序的链表中移除重复的项。

思路：可使用额外的空间的话，可以用数组存数字，实现最好的方式就是哈希表啦。遍历一下即可。

实现：

std::<span class="hljs-stl_container" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; background: transparent;"><span class="hljs-built_in" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(0, 134, 179); background: transparent;">map</span><Node*, <span class="hljs-keyword" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(149, 65, 33); background: transparent;">bool</span>></span>hash;
<span class="hljs-function" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; background: transparent;"><span class="hljs-keyword" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(149, 65, 33); background: transparent;">void</span> <span class="hljs-title" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(25, 70, 157); background: transparent;">duplicate_remove</span><span class="hljs-params" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(0, 0, 255); background: transparent;">(Node *node)</span></span>{<span class="hljs-keyword" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(149, 65, 33); background: transparent;">if</span>(!node)   <span class="hljs-keyword" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(149, 65, 33); background: transparent;">return</span> ;Node *post=node->next;hash[node->data] = <span class="hljs-keyword" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(149, 65, 33); background: transparent;">true</span>;<span class="hljs-keyword" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(149, 65, 33); background: transparent;">while</span>(post){<span class="hljs-keyword" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(149, 65, 33); background: transparent;">if</span>(hash[post->data]){Node *temp = post;post = post->next;node->next = post;<span class="hljs-keyword" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(149, 65, 33); background: transparent;">delete</span> temp;}<span class="hljs-keyword" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(149, 65, 33); background: transparent;">else</span>{hash[post->data] = <span class="hljs-keyword" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(149, 65, 33); background: transparent;">true</span>;node = post;post = post->next;}}
}

如果不允许使用临时缓存，怎么解决？

思路：用两个指针。当某个指针指向某个元素时，另一个指针将后面的相同元素全部删除。复杂度O(n^2)。具体实现就不写了。

12、链表求和问题。

该问题基本上有两个类型：

a、1->2->5->4 , 2->5->3->4,得3->7->8->8.

思路：先加高位，再加低位。两个0~9的数相加，要么不进位，要么进位为1.用两个指针，p指向当前进位点，q指向当前操作点。当然第一个元素得特殊考虑，可能进位嘛。

自己实现：

Node* merge_list_add(Node *list1,Node *list2){Node*q1=list1,*q2=list2,*ans=NULL,*pre=NULL,*p=NULL,*q=NULL;<span class="hljs-keyword" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(149, 65, 33); background: transparent;">int</span> cvalue = q1->data+ q2->data;<span class="hljs-keyword" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(149, 65, 33); background: transparent;">bool</span> flag = <span class="hljs-keyword" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(149, 65, 33); background: transparent;">false</span>;ans = <span class="hljs-keyword" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(149, 65, 33); background: transparent;">new</span> Node();<span class="hljs-comment" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: italic; font-family: inherit; vertical-align: baseline; color: rgb(64, 128, 128); background: transparent;">// node 1</span><span class="hljs-keyword" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(149, 65, 33); background: transparent;">if</span>(cvalue ><span class="hljs-number" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(64, 160, 112); background: transparent;">9</span>){ <span class="hljs-comment" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: italic; font-family: inherit; vertical-align: baseline; color: rgb(64, 128, 128); background: transparent;">//进位</span>pre = <span class="hljs-keyword" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(149, 65, 33); background: transparent;">new</span> Node();pre->data =cvalue%<span class="hljs-number" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(64, 160, 112); background: transparent;">10</span>;ans->next = pre;ans->data = <span class="hljs-number" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(64, 160, 112); background: transparent;">1</span>;p=pre;}<span class="hljs-function" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; background: transparent;"><span class="hljs-keyword" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(149, 65, 33); background: transparent;">else</span> <span class="hljs-title" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(25, 70, 157); background: transparent;">if</span><span class="hljs-params" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(0, 0, 255); background: transparent;">(9 ==  cvalue)</span></span>{<span class="hljs-comment" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: italic; font-family: inherit; vertical-align: baseline; color: rgb(64, 128, 128); background: transparent;">//最高位为9</span>flag = <span class="hljs-keyword" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(149, 65, 33); background: transparent;">true</span>;ans->data =cvalue;pre= ans;p=pre;}<span class="hljs-keyword" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(149, 65, 33); background: transparent;">else</span>{ans->data =cvalue;p = pre= ans;}q1=q1->next;q2=q2->next;<span class="hljs-keyword" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(149, 65, 33); background: transparent;">while</span>(q1 && q2){<span class="hljs-comment" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: italic; font-family: inherit; vertical-align: baseline; color: rgb(64, 128, 128); background: transparent;">// the following node</span>q = <span class="hljs-keyword" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(149, 65, 33); background: transparent;">new</span> Node();pre->next = q;cvalue = q1->data+ q2->data;q->data =cvalue%<span class="hljs-number" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(64, 160, 112); background: transparent;">10</span>;<span class="hljs-keyword" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(149, 65, 33); background: transparent;">if</span>(cvalue > <span class="hljs-number" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(64, 160, 112); background: transparent;">9</span> ){<span class="hljs-keyword" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(149, 65, 33); background: transparent;">if</span>(flag){<span class="hljs-keyword" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(149, 65, 33); background: transparent;">if</span>(p != ans){p->data += <span class="hljs-number" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(64, 160, 112); background: transparent;">1</span>;}<span class="hljs-keyword" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(149, 65, 33); background: transparent;">else</span>{<span class="hljs-comment" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: italic; font-family: inherit; vertical-align: baseline; color: rgb(64, 128, 128); background: transparent;">//999...[],前面全是9</span>Node*temp = <span class="hljs-keyword" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(149, 65, 33); background: transparent;">new</span> Node();temp->data= <span class="hljs-number" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(64, 160, 112); background: transparent;">1</span>;temp->next= ans;flag =<span class="hljs-keyword" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(149, 65, 33); background: transparent;">false</span>;ans =temp;p = ans;}}<span class="hljs-keyword" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(149, 65, 33); background: transparent;">else</span>{p->data +=<span class="hljs-number" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(64, 160, 112); background: transparent;">1</span>;}<span class="hljs-keyword" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(149, 65, 33); background: transparent;">for</span>(p=p->next;p!=q;p=p->next){p->data =<span class="hljs-number" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(64, 160, 112); background: transparent;">0</span>;}}<span class="hljs-function" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; background: transparent;"><span class="hljs-keyword" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(149, 65, 33); background: transparent;">else</span> <span class="hljs-title" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(25, 70, 157); background: transparent;">if</span><span class="hljs-params" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(0, 0, 255); background: transparent;">(cvalue <9)</span></span>{p = q;}pre = q;q1=q1->next;q2=q2->next;}<span class="hljs-keyword" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(149, 65, 33); background: transparent;">return</span> ans;
}

参考：http://hawstein.com/posts/add-singly-linked-list.html,第二种实现不错

b、元素个数不一定相同，高位在后，个位在链表头结点。1->2->3 , 4->5->3->4，得5->7->6->4.

思路：需要注意的是，链表为空，有进位，链表长度不一样。

<span class="hljs-preprocessor" style="border: 0px; margin: 0px; padding: 0px; font-weight: bold; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(153, 153, 153); background: transparent;">#<span class="hljs-keyword" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(149, 65, 33); background: transparent;">include</span> <assert.h></span>
<span class="hljs-preprocessor" style="border: 0px; margin: 0px; padding: 0px; font-weight: bold; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(153, 153, 153); background: transparent;">#<span class="hljs-keyword" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(149, 65, 33); background: transparent;">include</span> <iostream></span>
<span class="hljs-keyword" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(149, 65, 33); background: transparent;">using</span> <span class="hljs-keyword" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(149, 65, 33); background: transparent;">namespace</span> <span class="hljs-built_in" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(0, 134, 179); background: transparent;">std</span>;
<span class="hljs-keyword" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(149, 65, 33); background: transparent;">struct</span> Node{<span class="hljs-keyword" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(149, 65, 33); background: transparent;">int</span> data;Node *next;
};
Node* create_list(<span class="hljs-keyword" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(149, 65, 33); background: transparent;">int</span> arr[],<span class="hljs-keyword" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(149, 65, 33); background: transparent;">int</span> len){assert(arr &&len><span class="hljs-number" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(64, 160, 112); background: transparent;">0</span>);Node *head =  <span class="hljs-keyword" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(149, 65, 33); background: transparent;">new</span> Node();head->data = arr[<span class="hljs-number" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(64, 160, 112); background: transparent;">0</span>];Node *cur=NULL;Node *pre=head;<span class="hljs-keyword" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(149, 65, 33); background: transparent;">for</span>(<span class="hljs-keyword" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(149, 65, 33); background: transparent;">int</span> i=<span class="hljs-number" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(64, 160, 112); background: transparent;">1</span>;i<len;++i){cur = <span class="hljs-keyword" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(149, 65, 33); background: transparent;">new</span> Node();cur->data =arr[i];pre->next = cur;pre = cur;}cur->next = NULL;<span class="hljs-keyword" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(149, 65, 33); background: transparent;">return</span> head;
}
Node* merge_list_add(Node *list1,Node *list2){<span class="hljs-keyword" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(149, 65, 33); background: transparent;">if</span>(NULL == list1) returnlist2;<span class="hljs-keyword" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(149, 65, 33); background: transparent;">if</span>(NULL == list2) returnlist1;Node *ans=NULL,*pre=NULL;<span class="hljs-keyword" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(149, 65, 33); background: transparent;">int</span> c=<span class="hljs-number" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(64, 160, 112); background: transparent;">0</span>;<span class="hljs-comment" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: italic; font-family: inherit; vertical-align: baseline; color: rgb(64, 128, 128); background: transparent;">//进位</span><span class="hljs-keyword" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(149, 65, 33); background: transparent;">int</span> value = <span class="hljs-number" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(64, 160, 112); background: transparent;">0</span>;<span class="hljs-keyword" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(149, 65, 33); background: transparent;">while</span>(list1 &&list2){value =list1->data +list2->data + c;Node* temp = newNode();temp->data =value%<span class="hljs-number" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(64, 160, 112); background: transparent;">10</span>;c = value/<span class="hljs-number" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(64, 160, 112); background: transparent;">10</span>;<span class="hljs-keyword" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(149, 65, 33); background: transparent;">if</span>(pre){pre->next =temp;pre = temp;}<span class="hljs-keyword" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(149, 65, 33); background: transparent;">else</span>ans=pre=temp;list2 = list2->next;list1 =list1->next;}  <span class="hljs-keyword" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(149, 65, 33); background: transparent;">if</span>(!list1 &&!list2 && c><span class="hljs-number" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(64, 160, 112); background: transparent;">0</span>){<span class="hljs-comment" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: italic; font-family: inherit; vertical-align: baseline; color: rgb(64, 128, 128); background: transparent;">//两个链表长度一样，但有进位</span>Node* temp = newNode();temp->data = <span class="hljs-number" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(64, 160, 112); background: transparent;">1</span>;temp->next =NULL;<span class="hljs-comment" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: italic; font-family: inherit; vertical-align: baseline; color: rgb(64, 128, 128); background: transparent;">//结束</span>pre->next = temp;}<span class="hljs-comment" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: italic; font-family: inherit; vertical-align: baseline; color: rgb(64, 128, 128); background: transparent;">//有一个链表更长</span><span class="hljs-keyword" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(149, 65, 33); background: transparent;">while</span>(list1){value =list1->data + c;Node* temp = newNode();temp->data =value%<span class="hljs-number" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(64, 160, 112); background: transparent;">10</span>;c = value/<span class="hljs-number" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(64, 160, 112); background: transparent;">10</span>;pre->next = temp;pre = temp;list1 =list1->next;   }<span class="hljs-keyword" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(149, 65, 33); background: transparent;">while</span>(list2){value =list2->data + c;Node* temp = newNode();temp->data =value%<span class="hljs-number" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(64, 160, 112); background: transparent;">10</span>;c = value/<span class="hljs-number" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(64, 160, 112); background: transparent;">10</span>;pre->next = temp;pre = temp;list2 =list2->next;   }pre->next = NULL;<span class="hljs-keyword" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(149, 65, 33); background: transparent;">return</span> ans;
}
<span class="hljs-function" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; background: transparent;"><span class="hljs-keyword" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(149, 65, 33); background: transparent;">int</span> <span class="hljs-title" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(25, 70, 157); background: transparent;">main</span><span class="hljs-params" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(0, 0, 255); background: transparent;">()</span></span>{<span class="hljs-keyword" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(149, 65, 33); background: transparent;">int</span> a[]={<span class="hljs-number" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(64, 160, 112); background: transparent;">1</span>,<span class="hljs-number" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(64, 160, 112); background: transparent;">2</span>,<span class="hljs-number" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(64, 160, 112); background: transparent;">7</span>};<span class="hljs-keyword" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(149, 65, 33); background: transparent;">int</span> b[]={<span class="hljs-number" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(64, 160, 112); background: transparent;">4</span>,<span class="hljs-number" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(64, 160, 112); background: transparent;">5</span>,<span class="hljs-number" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(64, 160, 112); background: transparent;">3</span>,<span class="hljs-number" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(64, 160, 112); background: transparent;">9</span>,<span class="hljs-number" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(64, 160, 112); background: transparent;">3</span>};<span class="hljs-comment" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: italic; font-family: inherit; vertical-align: baseline; color: rgb(64, 128, 128); background: transparent;">//此处应该加个判断，保证数组元素均在[0,9]</span>Node* lista =create_list(a,<span class="hljs-number" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(64, 160, 112); background: transparent;">3</span>);Node* listb =create_list(b,<span class="hljs-number" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(64, 160, 112); background: transparent;">5</span>);Node* cur = lista;<span class="hljs-built_in" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(0, 134, 179); background: transparent;">cout</span><<<span class="hljs-string" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(33, 145, 97); background: transparent;">"list a:"</span>;<span class="hljs-keyword" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(149, 65, 33); background: transparent;">while</span>(cur != NULL){<span class="hljs-built_in" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(0, 134, 179); background: transparent;">cout</span><<cur->data<<<span class="hljs-string" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(33, 145, 97); background: transparent;">""</span>;cur = cur->next;}cur = listb;<span class="hljs-built_in" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(0, 134, 179); background: transparent;">cout</span><<endl<<<span class="hljs-string" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(33, 145, 97); background: transparent;">"listb: "</span>;<span class="hljs-keyword" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(149, 65, 33); background: transparent;">while</span>(cur != NULL){<span class="hljs-built_in" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(0, 134, 179); background: transparent;">cout</span><<cur->data<<<span class="hljs-string" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(33, 145, 97); background: transparent;">""</span>;cur = cur->next;}<span class="hljs-built_in" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(0, 134, 179); background: transparent;">cout</span><<endl;Node *ans =merge_list_add(lista, listb);<span class="hljs-keyword" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(149, 65, 33); background: transparent;">for</span>(; ans; ans=ans->next)<span class="hljs-built_in" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(0, 134, 179); background: transparent;">cout</span><<ans->data<<<span class="hljs-string" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(33, 145, 97); background: transparent;">" "</span>;<span class="hljs-built_in" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(0, 134, 179); background: transparent;">cout</span><<endl;
}

13、用算法实现删除链表的一个中间节点，所知的只有该节点的指针。如a-b-c-d-e中只知道c的指针，实现a-b-d-e。

思路：若直接删除的话，链表就断了，可是无法得到节点c的前驱b。故可转换思路利用c的后继d。将d的值赋给c，然后将后继节点d删除，也就实现删除操作。

由于c的位置不定，得分情况讨论。一、c为普通的中间节点，用上述方式解决。二，c为头节点，用上述方式解决。三、c为尾节点，一般认为删除即可，但是会出现问题。删除之后，尾节点的前驱不为空，下次遍历就会出错，特别注意。四、c为空节点，直接返回。

实现：

<span class="hljs-function" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; background: transparent;"><span class="hljs-keyword" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(149, 65, 33); background: transparent;">bool</span> <span class="hljs-title" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(25, 70, 157); background: transparent;">remove_elem</span><span class="hljs-params" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(0, 0, 255); background: transparent;">(Node* node)</span></span>{<span class="hljs-keyword" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(149, 65, 33); background: transparent;">if</span>(!node || !node->next)    returnfalse;Node *post = node->next;node->data = post->data;node->next = post->next;<span class="hljs-keyword" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(149, 65, 33); background: transparent;">delete</span> post;<span class="hljs-keyword" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(149, 65, 33); background: transparent;">return</span> <span class="hljs-keyword" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(149, 65, 33); background: transparent;">true</span>;
}

扩展：

a、Google题目，给定单向链表的头指针和一个结点指针，定义一个函数在O(1)时间删除该结点。

思路跟前面的一致，同样要注意尾节点。

b、只给定单链表中某个结点p(非空结点)，在p前面插入一个结点。

思路：首先分配一个结点q，将q插入在p后，接下来将p中的数据copy入q中，
然后再将要插入的数据记录在p中。

14、环链表开始节点，1->2->5->4->2

思路：

1、用快慢指针，满指针1，快指针2。

我们注意到第一次相遇时，指针走过的路程S1 = 非环部分长度 + 弧A长

快指针走过的路程S2 = 非环部分长度 + n * 环长 + 弧A长

S1 * 2 = S2，可得非环部分长度 = n * 环长 - 弧A长

让指针1到起始点后，走过一个非环部分长度，指针2过了相等的长度。

就是n * 环长 - 弧A长，正好回到环的开头。

或者参考：http://blog.csdn.net/lalor/article/details/7628332

2、更简单直观的方法就是利用哈希表。无环的话，每个地址就是不一样；有环的话，两个地址一样的就是环开始节点。下面用c++的map实现

std::map<Node*, bool>hash;

Node* loop_start(Node* node){

while(node){

if(hash(node))

return node;

else{

hash(node) = true;

node = node->next;

}

return NULL; //return head ; same

}

15、如何知道环的长度

一、在环上相遇后，记录第一次相遇点为pos，之后指针slow继续每次走1步，fast每次走2步。在下次相遇的时候fast比slow正好又多走了一圈，也就是多走的距离等于环长。

　　设从第一次相遇到第二次相遇，设slow走了len步，则fast走了2*len步，相遇时多走了一圈：环长=2*len-len。

二、利用哈希表，即两个碰撞元素间的个数

16、输入一个链表的头结点，从尾到头反过来打印出每个结点的值。

思路：用栈实现。

进阶：用递归。实现如下：

<span class="hljs-function" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; background: transparent;"><span class="hljs-keyword" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(149, 65, 33); background: transparent;">void</span> <span class="hljs-title" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(25, 70, 157); background: transparent;">PrintListReversingly</span><span class="hljs-params" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(0, 0, 255); background: transparent;">(ListNode*pHead)</span></span>{<span class="hljs-keyword" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(149, 65, 33); background: transparent;">if</span>(pHead != NULL){<span class="hljs-keyword" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(149, 65, 33); background: transparent;">if</span>(pHead->m_pNext != NULL){PrintListReversingly(pHead->m_pNext);}<span class="hljs-built_in" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(0, 134, 179); background: transparent;">printf</span>(<span class="hljs-string" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(33, 145, 97); background: transparent;">"%d\t"</span>,pHead->m_nValue);}
}

注意：但使用递归就意味着可能发生栈溢出的风险，尤其是链表非常长的时候。所以，基于循环实现的栈的鲁棒性要好一些。

17、输入两个递增链表，合并为一个递增链表。

思路：遍历两个链表，依次比较，形成新的队列

进阶：递归，每次递归返回合并后新链表的头结点

list_node*List::recursive_merge(list_node * a,list_node * b){<span class="hljs-keyword" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(149, 65, 33); background: transparent;">if</span>(a == NULL)<span class="hljs-keyword" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(149, 65, 33); background: transparent;">return</span> b;<span class="hljs-keyword" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(149, 65, 33); background: transparent;">if</span>(b == NULL)<span class="hljs-keyword" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(149, 65, 33); background: transparent;">return</span> a;<span class="hljs-keyword" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(149, 65, 33); background: transparent;">if</span>(a->value <= b->value){a->next=recursive_merge(a->next,b);<span class="hljs-keyword" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(149, 65, 33); background: transparent;">return</span> a;}<span class="hljs-keyword" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(149, 65, 33); background: transparent;">if</span>(a->value > b->value){b->next=recursive_merge(a,b->next);<span class="hljs-keyword" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(149, 65, 33); background: transparent;">return</span> b;}
}

18、用链表实现约瑟夫环

这里就不实现了。

19、判断一条单向链表是不是“回文”，1-2-4-2-1

思路：对于单链表结构，可以用两个指针从两端或者中间遍历并判断对应字符是否相等。但这里的关键就是如何朝两个方向遍历。

由于单链表是单向的，所以要向两个方向遍历的话，可以采取经典的快慢指针的方法，即定位到链表的中间位置，再将链表的后半逆置，最后用两个指针同时从链表头部和中间开始同时遍历并比较即可。

实现：（注意链表元素的奇偶性，稍微不同）

<span class="hljs-function" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; background: transparent;"><span class="hljs-keyword" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(149, 65, 33); background: transparent;">bool</span> <span class="hljs-title" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(25, 70, 157); background: transparent;">is_list_plalindrome</span><span class="hljs-params" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(0, 0, 255); background: transparent;">(Node*head)</span></span>{<span class="hljs-keyword" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(149, 65, 33); background: transparent;">if</span>(!head)<span class="hljs-keyword" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(149, 65, 33); background: transparent;">return</span> <span class="hljs-keyword" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(149, 65, 33); background: transparent;">false</span>;Node *one=head,*two=head,*pre=NULL;<span class="hljs-keyword" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(149, 65, 33); background: transparent;">while</span>(two!=NULL && two->next!=NULL){pre=one;one = one->next;two = two->next->next;}<span class="hljs-comment" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: italic; font-family: inherit; vertical-align: baseline; color: rgb(64, 128, 128); background: transparent;">//if length of list is odd, mid</span>Node *subhead=NULL,*node=NULL,*post=NULL;<span class="hljs-keyword" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(149, 65, 33); background: transparent;">if</span>(!two){ <span class="hljs-comment" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: italic; font-family: inherit; vertical-align: baseline; color: rgb(64, 128, 128); background: transparent;">//even,two==NULL</span>subhead = one;}<span class="hljs-keyword" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(149, 65, 33); background: transparent;">else</span>{ <span class="hljs-comment" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: italic; font-family: inherit; vertical-align: baseline; color: rgb(64, 128, 128); background: transparent;">//odd</span>subhead=one->next;}node=subhead;post=node->next;<span class="hljs-keyword" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(149, 65, 33); background: transparent;">while</span>(node->next){<span class="hljs-comment" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: italic; font-family: inherit; vertical-align: baseline; color: rgb(64, 128, 128); background: transparent;">// rotate sublist （旋转的这种写法，很容易理解）</span>node->next = post->next;post->next = subhead;subhead = post;post = node->next;}<span class="hljs-keyword" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(149, 65, 33); background: transparent;">for</span>(Node*p=head,*q=subhead;p!=pre->next;p=p->next,q=q->next){<span class="hljs-keyword" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(149, 65, 33); background: transparent;">if</span>(p->data!=q->data)<span class="hljs-keyword" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(149, 65, 33); background: transparent;">return</span> <span class="hljs-keyword" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(149, 65, 33); background: transparent;">false</span>;}<span class="hljs-keyword" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(149, 65, 33); background: transparent;">return</span> <span class="hljs-keyword" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(149, 65, 33); background: transparent;">true</span>;
}

20、从尾到头输出链表。

题目：输入一个链表的头结点，从尾到头反过来输出每个结点的值。

思路：跟输出倒数第n个元素的方法类似。

方法一、先把链表反向，然后再从头到尾遍历一遍。但该方法需要额外的操作

方法二、设一个栈，从头到尾遍历一次，把结点值压力栈中，再出栈打印。

方法三、递归。

实现：

<span class="hljs-function" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; background: transparent;"><span class="hljs-keyword" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(149, 65, 33); background: transparent;">void</span> <span class="hljs-title" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(25, 70, 157); background: transparent;">list_out_reverse</span><span class="hljs-params" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(0, 0, 255); background: transparent;">(Node*head)</span></span>{<span class="hljs-keyword" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(149, 65, 33); background: transparent;">if</span>(!head)<span class="hljs-keyword" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(149, 65, 33); background: transparent;">return</span>;<span class="hljs-function" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; background: transparent;"><span class="hljs-keyword" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(149, 65, 33); background: transparent;">else</span><span class="hljs-title" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(25, 70, 157); background: transparent;">list_out_reverse</span><span class="hljs-params" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(0, 0, 255); background: transparent;">(head->next)</span></span>;<span class="hljs-built_in" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(0, 134, 179); background: transparent;">cout</span><<head->data<<<span class="hljs-string" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(33, 145, 97); background: transparent;">" "</span>;
}

扩展：该题还有两个常见的变体：

1. 从尾到头输出一个字符串；

2. 定义一个函数求字符串的长度，要求该函数体内不能声明任何变量。

两个的分别实现：

<span class="hljs-function" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; background: transparent;"><span class="hljs-keyword" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(149, 65, 33); background: transparent;">void</span> <span class="hljs-title" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(25, 70, 157); background: transparent;">reverseString</span><span class="hljs-params" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(0, 0, 255); background: transparent;">(conststring& s,<span class="hljs-keyword" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(149, 65, 33); background: transparent;">unsigned</span> <span class="hljs-keyword" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(149, 65, 33); background: transparent;">int</span> begin)</span></span>{<span class="hljs-keyword" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(149, 65, 33); background: transparent;">if</span>(!s.size())<span class="hljs-keyword" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(149, 65, 33); background: transparent;">return</span>;<span class="hljs-keyword" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(149, 65, 33); background: transparent;">if</span>(begin>=s.size())<span class="hljs-keyword" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(149, 65, 33); background: transparent;">return</span>;reverseString(s,begin+<span class="hljs-number" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(64, 160, 112); background: transparent;">1</span>);<span class="hljs-built_in" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(0, 134, 179); background: transparent;">cout</span><<s[begin]<<<span class="hljs-string" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(33, 145, 97); background: transparent;">" "</span>;
}

<span class="hljs-function" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; background: transparent;"><span class="hljs-keyword" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(149, 65, 33); background: transparent;">int</span> <span class="hljs-title" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(25, 70, 157); background: transparent;">getLength</span><span class="hljs-params" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(0, 0, 255); background: transparent;">(<span class="hljs-keyword" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(149, 65, 33); background: transparent;">const</span> <span class="hljs-keyword" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(149, 65, 33); background: transparent;">char</span> *s)</span></span>{<span class="hljs-keyword" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(149, 65, 33); background: transparent;">if</span>(*s==<span class="hljs-string" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(33, 145, 97); background: transparent;">'/0'</span>)<span class="hljs-keyword" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(149, 65, 33); background: transparent;">return</span> <span class="hljs-number" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(64, 160, 112); background: transparent;">0</span>;<span class="hljs-keyword" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(149, 65, 33); background: transparent;">return</span> getLength(s+<span class="hljs-number" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(64, 160, 112); background: transparent;">1</span>) + <span class="hljs-number" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(64, 160, 112); background: transparent;">1</span>;
}

21、链表和数组的区别？

分析：主要在基本概念上的理解。但是最好能考虑的全面一点，现在公司招人的竞争可能就在细节上产生，谁比较仔细，谁获胜的机会就大。

数组无需初始化，因为数组的元素在内存的栈区，系统自动申请空间。而链表的结点元素在内存的堆区，每个元素须手动申请空间，如malloc。也就是说数组是静态分配内存，而链表是动态分配内存。链表如此麻烦为何还要用链表呢？数组不能完全代替链表吗？回到这个问题只需想想我们当初是怎么完成学生信息管理系统的。为何那时候要用链表？因为学生管理系统中的插入，删除等操作都很灵活，而数组则大小固定，也无法灵活高效的插入，删除。

数组是线性结构，静态分配内存，在内存中连续，数组元素在栈区。可以直接索引，时间复杂度O(1)。数组插入或删除元素比较困难，时间复杂度O(n)。

链表也是线性结构，动态分配内存，在内存中不连续，链表元素在堆区。元素的定位均需遍历，时间复杂度O(n)。链表插入或删除元素操作灵活性强，时间复杂度O(1)。

22、编写实现链表排序的一种算法。说明为什么你会选择用这样的方法？

思路：如果只是数据内容之间的相互交换，那么这种排序方法也比较适合链表的排序，插入、冒泡、希尔和选择排序。快速排序、合并排序、堆排序都涉及到了中间值的选取问题，所以不大适合链表排序。

选择排序的实现：

Node* insert_sort(Node *head){<span class="hljs-keyword" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(149, 65, 33); background: transparent;">if</span>(!head ||!head->next)<span class="hljs-keyword" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(149, 65, 33); background: transparent;">return</span> head;Node *p,*q,*pre,*temp;p=head->next;head->next=NULL;<span class="hljs-comment" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: italic; font-family: inherit; vertical-align: baseline; color: rgb(64, 128, 128); background: transparent;">//   p is the head of unsorted list</span><span class="hljs-comment" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: italic; font-family: inherit; vertical-align: baseline; color: rgb(64, 128, 128); background: transparent;">//   head is the head of sorted list</span><span class="hljs-keyword" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(149, 65, 33); background: transparent;">while</span>(p){q=head;<span class="hljs-keyword" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(149, 65, 33); background: transparent;">while</span>(q &&(q->data < p->data)){pre=q;q=q->next;}temp = p->next;<span class="hljs-keyword" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(149, 65, 33); background: transparent;">if</span>(q==head){p->next = q;head = p;}<span class="hljs-keyword" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(149, 65, 33); background: transparent;">else</span>{pre->next=p;p->next = q;}p=temp;}<span class="hljs-keyword" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(149, 65, 33); background: transparent;">return</span> head;
}

其他排序参考：http://www.voidcn.com/blog/Hackbuteer1/article/p-999842.html

http://wenku.baidu.com/link?url=CxhR7E5PGrEwRU5eKu_3xX5EvZ6MP-7GhRLhAfoQFThh5HxlQ5SgIxdfRPVXRO-oeCkwFYFqLJJezeswxdOmRE4W_QJBY3iS4Xpot23XCPi

23、复杂链表的复制（默认无环）

Q:有一个复杂链表，其结点除了有一个m_pNext指针指向下一个结点外，还有一个m_pSibling指向链表中的任一结点或者NULL。请完成函数ComplexNode* Clone(ComplexNode* pHead)，以复制一个复杂链表。

一开始想这道题毫无思路，如果蛮来，首先创建好正常的链表，然后考虑sibling这个分量，则需要O(n^2)的时间复杂度。

思路一：一般复制一个简单链表就这么遍历一遍就好了，这个复杂链表，比简单链表多的地方就在于多了一个sibling的指针，也就是说在建立完简单链表之后，如何在新的链表中找到sibling对应的地址。我们已知的是旧的节点的地址，所以只需要用一个map，保存每一个节点旧的节点对应的新的节点的地址即可。（即将原链表中的结点N和相应复制结点N'建立哈希映射<N,N'>）

第一次遍历，建立简单节点，第二次遍历，对于旧链表中的每一个节点的sibling指针地址，从map中找到新链表中对应节点的地址，连接上就好了。

实现：（不错的实现，学习）

ComplexNode* Clone(ComplexNode*pHead){<span class="hljs-keyword" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(149, 65, 33); background: transparent;">if</span>(pHead == NULL)  <span class="hljs-keyword" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(149, 65, 33); background: transparent;">return</span> NULL;<span class="hljs-stl_container" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; background: transparent;"><span class="hljs-built_in" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(0, 134, 179); background: transparent;">map</span><ComplexNode*, ComplexNode*></span>pointMap;ComplexNode* newHead,*tail; <span class="hljs-comment" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: italic; font-family: inherit; vertical-align: baseline; color: rgb(64, 128, 128); background: transparent;">// newHead指向复制的新链表的开头，tail始终指向结尾</span><span class="hljs-comment" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: italic; font-family: inherit; vertical-align: baseline; color: rgb(64, 128, 128); background: transparent;">// 开辟一个头结点</span>newHead = <span class="hljs-keyword" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(149, 65, 33); background: transparent;">new</span> ComplexNode;newHead->value = pHead->value;newHead->pNext = NULL;newHead->pSibling = NULL;pointMap[pHead] = newHead; <span class="hljs-comment" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: italic; font-family: inherit; vertical-align: baseline; color: rgb(64, 128, 128); background: transparent;">// 将头结点放入map中</span>tail = newHead;ComplexNode *p = pHead->pNext;<span class="hljs-keyword" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(149, 65, 33); background: transparent;">while</span>(p != NULL){ <span class="hljs-comment" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: italic; font-family: inherit; vertical-align: baseline; color: rgb(64, 128, 128); background: transparent;">// 第一遍先将简单链表复制一下</span>ComplexNode* newNode = <span class="hljs-keyword" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(149, 65, 33); background: transparent;">new</span> ComplexNode;newNode->value = p->value;newNode->pNext = NULL;newNode->pSibling = NULL;tail->pNext = newNode;tail = newNode;pointMap[p] = newNode;p = p->pNext;}<span class="hljs-comment" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: italic; font-family: inherit; vertical-align: baseline; color: rgb(64, 128, 128); background: transparent;">// 根据map中保存的数据，找到对应的节点</span>p = pHead;tail = newHead;<span class="hljs-keyword" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(149, 65, 33); background: transparent;">while</span>(p!=NULL){<span class="hljs-keyword" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(149, 65, 33); background: transparent;">if</span>(p->pSibling!=NULL){tail->pSibling =pointMap.find(p->pSibling)->second;<span class="hljs-comment" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: italic; font-family: inherit; vertical-align: baseline; color: rgb(64, 128, 128); background: transparent;">//Key，找N对应的N’</span>}p = p->pNext;tail = tail->pNext;}<span class="hljs-keyword" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(149, 65, 33); background: transparent;">return</span> newHead;}

思路二：（精妙）一个技巧便可以巧妙的解答此题。看图便知。

首先是原始的链表

然后我们还是首先复制每一个结点N为N*，不同的是我们将N*让在对应的N后面，即为

然后我们要确定每一个N*的sibling分量，非常明显，N的sibling分量的next就是N*的sibling分量。

最后，将整个链表拆分成原始链表和拷贝出的链表。

这样，我们就解决了一个看似非常混乱和复杂的问题。

实现：

<span class="hljs-keyword" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(149, 65, 33); background: transparent;">struct</span> Node{<span class="hljs-keyword" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(149, 65, 33); background: transparent;">int</span> val;Node* next;Node*sibling;
};
<span class="hljs-function" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; background: transparent;"><span class="hljs-keyword" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(149, 65, 33); background: transparent;">void</span> <span class="hljs-title" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(25, 70, 157); background: transparent;">Clone</span><span class="hljs-params" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(0, 0, 255); background: transparent;">(Node* head)</span></span>{Node*current=head;<span class="hljs-keyword" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(149, 65, 33); background: transparent;">while</span>(current){Node*temp=<span class="hljs-keyword" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(149, 65, 33); background: transparent;">new</span> Node;temp->val=current->val;temp->next=current->next;temp->sibling=NULL;current->next=temp;current=temp->next;}
}
<span class="hljs-function" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; background: transparent;"><span class="hljs-keyword" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(149, 65, 33); background: transparent;">void</span> <span class="hljs-title" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(25, 70, 157); background: transparent;">ConstructSibling</span><span class="hljs-params" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(0, 0, 255); background: transparent;">(Node*head)</span></span>{Node*origin=head;Node*clone;<span class="hljs-keyword" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(149, 65, 33); background: transparent;">while</span>(origin){clone=origin->next;<span class="hljs-keyword" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(149, 65, 33); background: transparent;">if</span>(origin->sibling)clone->sibling=origin->sibling->next;origin=clone->next;}
}Node* Split(Node* head){Node*CloneHead,*clone,*origin;origin=head;<span class="hljs-keyword" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(149, 65, 33); background: transparent;">if</span>(origin){CloneHead=origin->next;origin->next=CloneHead->next;origin=CloneHead->next;clone=CloneHead;}<span class="hljs-keyword" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(149, 65, 33); background: transparent;">while</span>(origin){Node*temp=origin->next;origin->next=temp->next;origin=origin->next;clone->next=temp;clone=temp;}<span class="hljs-keyword" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: inherit; font-family: inherit; vertical-align: baseline; color: rgb(149, 65, 33); background: transparent;">return</span> CloneHead;
}
<span class="hljs-comment" style="border: 0px; margin: 0px; padding: 0px; font-weight: inherit; font-style: italic; font-family: inherit; vertical-align: baseline; color: rgb(64, 128, 128); background: transparent;">//the whole thing</span>
Clone(head);
ConstructSibling(head);
<p>Split(head);</p><p>
</p><p>转载自：http://www.voidcn.com/blog/ywok526/article/p-2520659.html</p>