线性表存储结构分为顺序存储、链式存储。
顺序存储的优点:
顺序存储的缺点:
链表就是典型的链式存储,将线性表L = (a0,a1,a2,........an-1)中个元素分布在存储器的不同存储块,成为结点(Node),通过地址或指针建立他们之间的练习,所得到的存储结构为链表结构。表中元素ai的结点形式如下:
其中,结点的data域存放数据元素ai,而next域是一个指针,指向ai的直接后继a(i+1)所在的结点。于是,线性表L=(a0,a1,......an-1)的结构如图:
一、节点类型描述:
- typedef struct node_t
- {
- data_t data; //节点的数据域
- struct node_t *next;//节点的后继指针域
- }linknode_t,*linklist_t;
也可这样表示:
- struct node_t
- {
- data_t data;
- struct node_t *next;
- }
- typedef struct node_t linknode_t;
- typedef struct node_t *linklist_t;
若说明
linknode_t A;
linklist_t p = &A;
则结构变量A为所描述的节点,而指针变量P为指向此类型节点的指针(p的值为节点的地址);
这样看来 linknode_t linklist_t 的作用是一样的,那为什么我们要定义两个数据类型(同一种)呢?主要为了代码的可读性,我们要求标识符要望文识义,便于理解;
1、linknode_t *pnode 指向一个节点;
2、linklist_t list 指向一个整体
二、头结点 head
我们在前篇提到的顺序存储线性表,如何表达一个空表{ },是通过list->last = -1来表现的,所谓的空表就是数据域为NULL,而我们的链表有数据域和指针域,我们如何表现空链表呢?这时,就引入了头结点的概念,头结点和其他节点数据类型一样,只是数据域为NULL,head->next = NULL,下面我们看一个创建空链表的函数,如何利用头结点来创建一个空链表:
- linklist_t CreateEmptyLinklist()
- {
- linklist_t list;
- list = (linklist_t)malloc(sizeof(linknode_t));
- if (NULL != list) {
- list->next = NULL;
- }
- return list;
- }
只要头结点,链表就还在!
三、链表基本运算的相关算法
链表的运算除了上面的创建空链表,还有数据的插入,删除,查找等函数,链表的运算有各种实现方法,如何写出一个高效的,封装性较好的函数是我们要考虑的,比如数据插入函数,我们就要尽可能考虑所有能出现的结果,比如:1)如果需插入数据的链表是个空表;2)所插入的位置超过了链表的长度;如果我们的函数能包含所有能出现的情况,不仅能大大提高我们的开发效率,也会减少代码的错误率。下面,我们来看看下面的这个链表的插入函数的实现:
- int InsertLinklist(linklist_t list, int at, data_t x)
- {
- linknode_t *node_prev, *node_at, *node_new;
- int pos_at;
- int found = 0;
- if (NULL == list) return -1;
- /* at must >= 0 */
- if (at < 0) return -1;
- /*第一步、分配空间*/
- node_new = malloc(sizeof(linknode_t));
- if (NULL == node_new)
- {
- return -1;
- }
- node_new->data = x; /* assigned value */
- node_new->next = NULL; /*节点如果插入超过链表长度的位置,会接到尾节点后面,这样,node_new成了尾节点,node_new->next = NULL */
- /*第二步、定位*/
- node_prev = list;//跟随指针,帮助我们更好的定位
- node_at = list->next; //遍历指针
- pos_at = 0;
- while (NULL != node_at)
- {
- if (pos_at == at)
- {
- found = 1; //找到正确的位置,跳出循环
- break;
- }
- /* move to the next pos_at */
- node_prev = node_at; //跟随指针先跳到遍历指针的位置
- node_at = node_at->next;//遍历指针跳到下一个节点的位置
- pos_at++;
- }
- /*第三步、插入*/
- if (found)
- {
- /* found = 1,找到正确的位置,插入 */
- node_new->next = node_at;//插入的节点next指向node_at
- node_prev->next = node_new;//插入节点的前一个节点
- }
- else
- {
- /*若是没找到正确的位置,即所插入位置超越了链表的长度,则接到尾节点的后面,同样,这样适用于{ }即空链表,这样我们可以建立一个空链表,利用这个函数,实现链表的初始化*/
- node_prev->next = node_new;
- }
这个插入函数可利用性就非常高。
下面讲一个完整链表代码贴出:
listlink.h
- #ifndef _LNK_LIST_H_
- #define _LNK_LIST_H_
- typedef int data_t;
- typedef struct node_t {
- data_t data;
- struct node_t *next;
- } linknode_t, *linklist_t;
- linklist_t CreateEmptyLinklist();
- void DestroyLinklist(linklist_t list);
- void ClearLinklist(linklist_t list);
- int EmptyLinklist(linklist_t list);
- int LengthLinklist(linklist_t list);
- int GetLinklist(linklist_t list, int at, data_t *x);
- int SetLinklist(linklist_t list, int at, data_t x);
- int InsertLinklist(linklist_t list, int at, data_t x);
- int DeleteLinklist(linklist_t list, int at);
- linklist_t ReverseLinklist(linklist_t list);
- #endif /* _LNK_LIST_H_ */
linklist.c
- #include <stdio.h>
- #include <stdlib.h>
- #include "linklist.h"
- linklist_t CreateEmptyLinklist()
- {
- linklist_t list;
- list = (linklist_t)malloc(sizeof(linknode_t));
- if (NULL != list) {
- list->next = NULL;
- }
- return list;
- }
- void DestroyLinklist(linklist_t list)
- {
- if (NULL != list) {
- ClearLinklist(list);
- free(list);
- }
- }
- void ClearLinklist(linklist_t list)
- {
- linknode_t *node; /* pointer to the node to be removed */
- if (NULL == list) return;
- while (NULL != list->next) {
- node = list->next;
- list->next = node->next;
- free(node);
- }
- return;
- }
- int LengthLinklist(linklist_t list)
- {
- int len = 0;
- linknode_t *node; //iterate pointer
- if (NULL == list) return -1;
- node = list->next; // node points to the first data node
- while (NULL != node) {
- len++;
- node = node->next;
- }
- return len;
- }
- int EmptyLinklist(linklist_t list)
- {
- if (NULL != list) {
- if (NULL == list->next) {
- return 1;
- } else {
- return 0;
- }
- } else {
- return -1;
- }
- }
- int GetLinklist(linklist_t list, int at, data_t *x)
- {
- linknode_t *node; /* used for iteration */
- int pos; /* used for iteration and compare with */
- if (NULL == list) return -1;
- /* at must >= 0 */
- if (at < 0) return -1;
- /* start from the first element */
- node = list->next;
- pos = 0;
- while (NULL != node) {
- if (at == pos) {
- if (NULL != x) {
- *x = node->data;
- }
- return 0;
- }
- /* move to the next */
- node = node->next;
- pos++;
- }
- return -1;
- }
- int SetLinklist(linklist_t list, int at, data_t x)
- {
- linknode_t *node; /* used for iteration */
- int pos;
- int found = 0;
- if (!list) return -1;
- /* at must >= 0 */
- if (at < 0) return -1;
- /* start from the first element */
- node = list->next;
- pos = 0;
- while (NULL != node) {
- if (at == pos) {
- found = 1; /* found the position */
- node->data = x;
- break;
- }
- /* move to the next */
- node = node->next;
- pos++;
- }
- if (1 == found) {
- return 0;
- } else {
- return -1;
- }
- }
- int InsertLinklist(linklist_t list, int at, data_t x)
- {
- /*
- * node_at and pos_at are used to locate the position of node_at.
- * node_prev follows the node_at and always points to previous node
- * of node_at.
- * node_new is used to point to the new node to be inserted.
- */
- linknode_t *node_prev, *node_at, *node_new;
- int pos_at;
- int found = 0;
- if (NULL == list) return -1;
- /* at must >= 0 */
- if (at < 0) return -1;
- node_new = malloc(sizeof(linknode_t));
- if (NULL == node_new) {
- return -1;
- }
- node_new->data = x; /* assigned value */
- node_new->next = NULL;
- node_prev = list;
- node_at = list->next;
- pos_at = 0;
- while (NULL != node_at) {
- if (pos_at == at) {
- /*
- * found the node 'at'
- */
- found = 1;
- break;
- }
- /* move to the next pos_at */
- node_prev = node_at;
- node_at = node_at->next;
- pos_at++;
- }
- if (found) {
- /* insert */
- node_new->next = node_at;
- node_prev->next = node_new;
- } else {
- /*
- * If not found, means the provided "at"
- * exceeds the upper limit of the list, just
- * append the new node to the end of the list.
- */
- node_prev->next = node_new;
- }
- return 0;
- }
- int DeleteLinklist(linklist_t list, int at)
- {
- /*
- * node_at and pos_at are used to locate the position of node_at.
- * node_prev follows the node_at and always points to previous node
- * of node_at.
- */
- linknode_t *node_prev, *node_at;
- int pos_at;
- int found = 0;
- if (!list) return -1;
- /* at must >= 0 */
- if (at < 0) return -1;
- node_prev = list;
- node_at = list->next;
- pos_at = 0;
- while (NULL != node_at) {
- if (pos_at == at) {
- /*
- * found the node 'at'
- */
- found = 1;
- break;
- }
- /* move to the next pos_at */
- node_prev = node_at;
- node_at = node_at->next;
- pos_at++;
- }
- if (found) {
- /* remove */
- node_prev->next = node_at->next;
- free(node_at);
- return 0;
- } else {
- return -1;
- }
- }
- linklist_t ReverseLinklist(linklist_t list)
- {
- linknode_t *node; /* iterator */
- linknode_t *node_prev; /* previous node of iterator */
- linknode_t *node_next; /* next node of iterator,
- * used to backup next of iterator
- */
- if (NULL == list) return NULL;
- node_prev = NULL;
- node = list->next;
- while (NULL != node) {
- /*
- * step1: backup node->next
- * due to the next of iterator will be
- * modified in step2
- */
- node_next = node->next;
- /*
- * when iterator reaches the last node
- * of original list, make the list head
- * point to the last node, so the original
- * last one becomes the first one.
- */
- if (NULL == node_next) {
- list->next = node;
- }
- /*
- * step2: reverse the linkage between nodes
- * make the node pointer to the previous node,
- * not the next node
- */
- node->next = node_prev;
- /*
- * step3: move forward
- */
- node_prev = node;
- node = node_next;
- }
- return list;
- }
main.c
- #include <stdio.h>
- #include <stdlib.h>
- #include "linklist.h"
- int main()
- {
- int i;
- data_t x;
- linklist_t p;
- p = CreateEmptyLinklist();
- data_t a[10] = {1,3,5,7,9,11,13,15,17,19};
- for(i = 0;i < 10;i++)
- {
- InsertLinklist(p,i,a[i]);
- }
- ReverseLinklist(p);
- printf("The length of the list is:%d\n",LengthLinklist(p));
- GetLinklist(p,4,&x);
- printf("The NO.4 of this list is:%d\n",x);
- SetLinklist(p,4,100);
- GetLinklist(p,4,&x);
- printf("After updating!The No.4 0f this list is:%d\n",x);
- DeleteLinklist(p,4);
- printf("After updating!The length of the list is:%d\n",LengthLinklist(p));
- GetLinklist(p,4,&x);
- printf("After updating!The No.4 0f this list is:%d\n",x);
- ReverseLinklist(p);
- ClearLinklist(p);
- if(EmptyLinklist(p))
- printf("This list is empty!\n");
- DestroyLinklist(p);
- printf("This list is destroyed!\n");
- return 0;
- }
执行结果如下:
- fs@ubuntu:~/qiang/list/list2$ ./Test
- The length of the list is:10
- The NO.4 of this list is:11
- After updating!The No.4 0f this list is:100
- After updating!The length of the list is:9
- After updating!The No.4 0f this list is:9
- This list is empty!
- This list is destroyed!