python数据结构——链表及其实现

一、单向链表

(1) 链表的定义

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

"""
链表的实现： list = [100, 200, 300]
   | 内存 | 数据区| 下一个节点地址|
地址1：0x11   100  0x34
地址2：0x34   200  0x20
地址3：0x20   300  None
那么列表实现就如图所示：
"""

(2)为什么需要链表

1. 顺序表的构建需要预先知道数据大小来申请一块连续的存储空间，而在进行扩充时又需要进行数据的搬迁，所以使用起来不是很灵活，引入链表结构可以充分利用计算机内存空间，实现灵活的动态管理。
2. 另外，如果现在需要存储一个较大的数据，连续的内存不够用，也可以采用链表进行分散的存储，然后将数据链接在一起。

(3)单向链表

1. 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，最后一个节点的链表域则指向一个空值。
2. 单向链表结点：
   
3. 单向链表：
   
4. 变量P指向链表的头结点的位置，从P出发能找到表中的任意结点

(4)单向循环列表

单向循环链表是将单向链表尾结点的next 指向头结点

(5)双向链表

1. 概述

双向链表或者双面链表，每个结点有两个链表，一个指向前一个结点，当此结点为第一个结点时，指向空，而另一个指向下一个结点，当此结点为最后一个结点时指向空值。
2. 双向链表结构 其中：P为前趋结点 N 为后继结点

二、单向链表实现

class Node(object):
    """节点"""
    def __init__(self, elem):
        super(Node, self).__init__()
        # 元素
        self.elem = elem
        # 下一个节点地址
        self.next = None


class SingleLinkList(object):
    """单链表：实现增、删、改、查"""
    def __init__(self, node=None):
        self.__head = node
   
    def is_empty(self):
        """链表为是否为空 """
        return self.__head is None

    def length(self):
        """链表长度"""
        cur = self.__head  # 定义游标cur,用来遍历节点
        count = 0  # 统计节点个数
        while cur is not None:
            count += 1
            cur = cur.next
        return count

    def travel(self):
        """ 遍历整个链表"""
        cur = self.__head
        while cur is not None:
            print("当前的节点是：%s" % cur.elem)
            cur = cur.next

    def add(self, item):
        """链表头部添加元素，头插法"""
        node = Node(item)
        node.next = self.__head
        self.__head = node

    def append(self, item):
        """链表尾部添加元素，尾插法"""
        node = Node(item)
        if self.is_empty():
            self.__head = node
        else:
            cur = self.__head
            while cur.next is not None:
                cur = cur.next
            cur.next = node

    def insert(self, pos, item):
        """
        指定位置添加元素 pos: 位置  item：元素
        pos: 从0开始
        """
        if pos <= 0:
            self.add(item)
        elif pos > (self.length() - 1):
            self.append(item)
        else:
            pre = self.__head  # 前一个位置
            count = 0
            while count < (pos - 1):
                count += 1
                pre = pre.next
            # 当循环退出后pre = pos -1 的位置
            node = Node(item)
            node.next = pre.next
            pre.next = node

    def remove(self, item):
        """
        删除节点 : 考虑列表为空，删除列表的头节点, 只有一个节点，尾部的节点
        """
        cur = self.__head
        pre = None
        while cur is not None:
            if cur.elem == item:
                # 判断次节点是否为头节点
                if cur == self.__head:
                    self.__head = cur.next
                else:
                    pre.next = cur.next
                break
            else:
                pre = cur
                cur = cur.next

    def search(self, item):
        """查找节点是否存在"""
        cur = self.__head
        while cur is not None:
            if cur.elem == item:
                return True
            else:
                cur = cur.next
        return False


if __name__ == '__main__':
    ll = SingleLinkList()
    print(ll.is_empty())
    ll.append(1)
    ll.append(100)
    ll.append(200)
    ll.travel()
    ll.remove(1)
    ll.travel()

二、单向循环列表实现

class Node(object):
    def __init__(self, item):
        """结点"""
        self.elem = item
        self.next = None


class SingleLinkCircle(object):
    """单向循环链表"""

    def __init__(self, node=None):
        self.__head = node
        if node:
            node.next = node

    def is_empty(self):
        """判断是否为空"""
        return self.__head is None

    def length(self):
        """判断链表长度"""
        if self.is_empty():
            return 0
        else:
            cur = self.__head
            count = 1
            while cur.next != self.__head:
                count += 1
                cur = cur.next
            return count

    def travel(self):
        """遍历链表"""
        if self.is_empty():
            print("")
        else:
            cur = self.__head
            while cur.next != self.__head:
                print(cur.elem, end=" ")
                cur = cur.next
            # 循环结束打印最后一个结点
            print(cur.elem)

    def add(self, item):
        """在头部添加结点"""
        node = Node(item)
        if self.is_empty():
            self.__head = node
            node.next = node
        else:
            cur = self.__head
            while cur.next != self.__head:
                cur = cur.next
            node.next = self.__head
            self.__head = node
            cur.next = node

    def append(self, item):
        """在尾部添加结点"""
        node = Node(item)
        if self.is_empty():
            self.__head = node
            node.next = self.__head
        else:
            cur = self.__head
            while cur.next != self.__head:
                cur = cur.next
            node.next = self.__head
            cur.next = node

    def insert(self, pos, item):
        """在特定位置插入结点"""
        if pos <= 0:
            self.add(item)
        elif pos > (self.length() - 1):
            self.append(item)
        else:
            pre = self.__head
            count = 0
            while count < (pos - 1):
                count += 1
                pre = pre.next
            node = Node(item)
            node.next = pre.next
            pre.next = node

    def remove(self, item):
        """删除指定结点"""
        cur = self.__head
        pre = None
        if self.is_empty():
            return
        while cur.next != self.__head:
            if cur.elem == item:
                # 头结点
                if cur == self.__head:
                    # 找到尾结点
                    finall = self.__head
                    while finall.next != self.__head:
                        finall = finall.next
                        # 将尾结点的地址指向要删除结点的下一个结点
                    finall.next = cur.next
                    self.__head = cur.next
                else:
                    # 中间结点
                    pre.next = cur.next
                return    #  这里注意，删除完成后让程序直接退出，不用break
            else:
                pre = cur
                cur = cur.next
        # 判断删除的是尾结点
        if cur.elem == item:
            if cur == self.__head:
                self.__head = None
            else:
                pre.next = self.__head

    def search(self, item):
        """查找结点"""
        if self.is_empty():
            return False
        else:
            cur = self.__head
            while cur.next != self.__head:
                if cur.elem == item:
                    return True
                cur = cur.next
            if cur.elem == item:
                return True
            return False


if __name__ == '__main__':
    ll = SingleLinkCircle()
    ll.add(3)
    ll.add(4)
    print("test add()\n")
    ll.travel()
    ll.append(5)
    ll.append(6)
    print("test append()\n")
    ll.travel()
    ll.insert(2, 9)
    ll.insert(3, 0)
    print("test insert()\n")
    ll.travel()
    ll.remove(4)
    ll.remove(6)
    print("test remove()\n")
    ll.travel()
    print("test search()\n")
    ll.search(5)
    print(ll.length())

三、双向链表实现

class Node(object):
    """node"""
    def __init__(self, item):
        self.elem = item
        self.prev = None
        self.next = None


class DoubleLinkList(object):
    def __init__(self, node=None):
        self.__head = node

    def is_empty(self):
        return self.__head is None

    def length(self):
        cur = self.__head
        count = 0
        while cur is not None:
            count += 1
            cur = cur.next
        return count

    def travel(self):
        cur = self.__head
        while cur is not None:
            print(cur.elem, end=" ")
            cur = cur.next
        print("")

    def add(self, item):
        node = Node(item)

        """method one"""
        # node.next = self.__head
        # self.__head = node
        # node.next.prev = node

        """method two"""
        self.__head.prev = node
        self.__head = node

    def append(self, item):
        node = Node(item)
        if self.is_empty():
            self.__head = node
        else:
            cur = self.__head
            while cur.next is not None:
                cur = cur.next
            cur.next = node
            node.prev = cur

    def insert(self, pos, item):
        node = Node(item)
        if pos <= 0:
            self.add(item)
        elif pos > (self.length()-1):
            self.append(item)
        else:
            cur = self.__head
            count = 0
            while count < pos:
                count += 1
                cur = cur.next
            # node.prev = cur
            # node.next = cur.next
            # cur = node
            # cur.next = node
            """ method"""
            node.next = cur
            node.prev = cur.prev
            cur.prev = node
            node.prev.next = node

    def remove(self, item):
        cur = self.__head
        while cur is not None:
            if cur.elem == item:
                if cur == self.__head:
                    self.__head = cur.next
                    if cur.next:
                        # only one node
                        cur.next.prev = None
                else:
                    cur.prev.next = cur.next
                    if cur.next:
                        # finally node
                        cur.next.prev = cur.prev
                break
            else:
                cur = cur.next

    def search(self, item):
        cur = self.__head
        while cur is not None:
            if cur.elem == item:
                return True
            else:
                cur = cur.next
        return False


if __name__ == '__main__':
    lk = DoubleLinkList()
    lk.append(2)
    lk.append(3)
    lk.insert(1, 0)
    lk.append(4)
    lk.append(5)
    lk.add(6)
    lk.travel()
    lk.remove(6)
    lk.travel()
    print(lk.length())