链表

链表的定义:

链表（Linked list）是一种常见的基础数据结构，是一种线性表，但是不像顺序表一样连续存储数据，而是在每一个节点（数据存储单元）里存放下一个节点的位置信息（即地址）。

单项链表

单向链表也叫单链表，是链表中最简单的一种形式，它的每个节点包含两个域，一个信息域（元素域）和一个链接域。这个链接指向链表中的下一个节点，而最后一个节点的链接域则指向一个空值。

• 表元素域elem用来存放具体的数据。
• 链接域next用来存放下一个节点的位置（python中的标识）
• 变量p指向链表的头节点（首节点）的位置，从p出发能找到表中的任意节点。

'''
单向链表单链表的操作
is_empty() 链表是否为空
length() 链表长度
travel() 遍历整个链表
add(item) 链表头部添加元素
append(item) 链表尾部添加元素
insert(pos, item) 指定位置添加元素
remove(item) 删除节点
search(item) 查找节点是否存在'''class Node(object):'''单向链表的节点'''def __init__(self, item):self.elem = itemself.next = Noneclass SingleLinkList(object):'''单链表'''def __init__(self):self.__head = Nonedef is_empty(self):'''链表是否为空'''return self.__head == Nonedef length(self):'''链表长度'''cur = self.__headcount = 0while cur != None:cur = cur.nextcount += 1return countdef travel(self):'''遍历整个链表'''cur = self.__headwhile cur != None:print(cur.elem, end=" ")cur = cur.nextprint("")def add(self, item):'''链表头部添加元素'''node = Node(item)node.next = self.__headself.__head = nodedef append(self, item):'''链表尾部添加元素'''cur = self.__headnode = Node(item)if cur == None:self.__head = nodeelse:while cur.next != None:cur = cur.nextcur.next = nodedef insert(self, pos, item):'''指定位置添加元素'''if pos <= 0:self.add(item)elif pos > (self.length() - 1):self.append(item)else:pre = self.__headcount = 0while count < (pos - 1):count += 1pre = pre.nextnode = Node(item)node.next = pre.nextpre.next = nodedef remove(self, item):'''删除节点'''cur = self.__headpre = Nonewhile cur != None:if cur.elem == item:# 判断是否是第一if pre == None:self.__head = cur.nextelse:pre.next = cur.nextbreakelse:pre = curcur = cur.nextdef search(self, item):'''查找节点是否存在'''cur = self.__headwhile cur != None:if cur.elem == item:return Truecur = cur.nextreturn FalsesingList = SingleLinkList()singList.add("a")
singList.add("b")
singList.append("c")
singList.append("d")
singList.append("e")
singList.append("f")
singList.append("g")print(singList.is_empty())
print(singList.length())
singList.travel()print("search", singList.search(1))singList.remove("b")singList.travel()singList.insert(3, 3)
singList.travel()

单向循环链表

单链表的一个变形是单向循环链表，链表中最后一个节点的next域不再为None，而是指向链表的头节点。

'''
单循环链表
'''
class Node(object):'''单向链表的节点'''def __init__(self, item):self.elem = itemself.next = Noneclass SingleCircleLinkList(object):'''单循环链表'''def __init__(self, node = None):self.__head = nodeif node:node.next = nodedef is_empty(self):'''链表是否为空'''return self.__head == Nonedef length(self):'''链表长度'''cur = self.__headcount = 1while cur.next != self.__head:count += 1cur = cur.nextreturn countdef travel(self):'''遍历整个链表'''cur = self.__headif cur == None:returnelse:while cur.next != self.__head:print(cur.elem, end=" ")cur = cur.nextprint(cur.elem)def add(self, item):'''链表头部添加元素'''cur = self.__headnode = Node(item)if cur == None:self.__head = nodenode.next = nodeelse:while cur.next != self.__head:cur = cur.nextnode.next = cur.nextself.__head = nodecur.next = nodedef append(self, item):'''链表尾部添加元素'''cur = self.__headnode = Node(item)if cur == None:self.__head = nodenode.next = nodeelse:while cur.next != self.__head:cur = cur.nextcur.next = nodenode.next = self.__headdef insert(self, pos, item):'''指定位置添加元素'''if pos <= 0:self.add(item)elif pos > (self.length() - 1):self.append(item)else:count = 0cur = self.__headpre = Nonenode = Node(item)while count < pos:count += 1pre = curcur = cur.nextnode.next = curpre.next = nodedef remove(self, item):'''删除节点''''''注意1、为空2、第一个节点的情况a) 列表只有一个节点b) 列表有多个节点3、在中间的情况'''if self.is_empty():return Nonecur = self.__headpre = Nonewhile cur.next != self.__head:if cur.elem == item:if cur == self.__head:rear = self.__headwhile rear.next != self.__head:rear = rear.nextself.__head = cur.nextrear.next = self.__headelse:pre.next = cur.nextreturnelse:pre = curcur = cur.next# 链表的最后一个元素if cur.elem == item:if pre == None:self.__head = Noneelse:pre.next = self.__headdef search(self, item):'''查找节点是否存在'''cur = self.__headif cur == None:return Falsewhile cur.next != self.__head:if cur.elem == item:return Truecur = cur.nextif cur.elem == item:return Truereturn Falsen = Node("1")
sc = SingleCircleLinkList()sc.add("a")
sc.add("b")
sc.add("c")
sc.add("d")
sc.add("e")
sc.add("f")
sc.append("11")
sc.insert(2, '22')sc.travel()sc.remove('f')
sc.travel()

双向链表

一种更复杂的链表是“双向链表”或“双面链表”。每个节点有两个链接：一个指向前一个节点，当此节点为第一个节点时，指向空值；而另一个指向下一个节点，当此节点为最后一个节点时，指向空值。

'''
双向链表
'''class Node(object):'''节点'''def __init__(self, item):self.elem = itemself.prev = Noneself.next = Noneclass DoubleLinkList(object):'''双向链表'''def __init__(self, node = None):self.__head = nodedef is_empty(self):'''链表是否为空'''return self.__head == Nonedef length(self):'''链表长度'''cur = self.__headcount = 0while cur != None:cur = cur.nextcount += 1return countdef travel(self):'''遍历整个链表'''cur = self.__headwhile cur != None:print(cur.elem, end=" ")cur = cur.nextprint("")def add(self, item):'''链表头部添加元素'''node = Node(item)if self.__head == None:self.__head = nodeelse:node.next = self.__headself.__head.prev = nodeself.__head = nodedef append(self, item):'''链表尾部添加元素'''node = Node(item)cur = self.__headif cur == None:self.__head = nodeelse:while cur.next != None:cur = cur.nextcur.next = nodenode.prev = curdef insert(self, pos, item):'''指定位置添加元素'''if pos <= 0:self.add(item)elif pos > (self.length() - 1):self.append(item)else:node = Node(item)cur = self.__headcount = 0while count < pos:count += 1cur = cur.nextnode.next = curnode.prev = cur.prevcur.prev = nodenode.prev.next = nodedef remove(self, item):'''删除节点'''cur = self.__headwhile cur != None:if cur.elem == item:if cur == self.__head:'''删除第一个元素'''self.__head = cur.nextif cur.next:cur.next.prev = Noneelse:cur.prev.next = cur.nextif cur.next:cur.next.prev = cur.prevreturnelse:cur = cur.nextdef search(self, item):'''查找节点是否存在'''cur = self.__headwhile cur != None:if cur.elem == item:return Truecur = cur.nextreturn Falsedl = DoubleLinkList()print("is_empty = ", dl.is_empty())
print("length  = ", dl.length())
dl.add("aa")
dl.add("bb")
dl.add("cc")
dl.append("dd")
dl.append("ee")dl.travel()# dl.remove("cc")
dl.remove("bb")
dl.remove('ee')
dl.travel()# print(dl.search("1"))dl.insert(0, "00")
dl.insert(2, '22')dl.travel()