python如何求链表的长度 链表 python

文章目录

• 前言
• 1. 双链表
• 2. 基本操作
• 3. 代码实现

前言

  本篇章主要介绍线性表中的双链表，并用Python实现其基本操作。

1. 双链表

prior指针指向其前驱结点，next指针指向其后继结点。

  双链表的结点定义如下：

class DoubleLinkNode(object):
    def __init__(self, data=None, prior=None, next=None):
        self.data = data
        self.prior = prior
        self.next = next

$O(1)$，但是我在下面的代码中传入的不是结点，而是整个链表按值或位插入或删除，所以复杂度仍为$O(n)$，重在算法的思想嘛，哈哈哈哈哈！

2. 基本操作

  双链表的插入和删除操作相比单链表，多了一个前驱指针的操作，注意不要乱了执行的顺序。

操作名称	操作说明
InsertInHead(val_list)	头插法创建双链表
InsertInTail(val_list)	尾插法创建双链表
IsEmpty()	判断双链表是否为空
LengthList()	返回双链表的长度
TraverseList()	打印出双链表里的数据元素
InsertInPosition(pos, data)	在指定位置插入
SearchWithPosition(pos)	按位置查找结点
SearchWithVal(data)	按值查找结点
RemoveWithPosition(pos)	移除指定位置的结点
RemoveWithVal(data)	移除指定值的结点

3. 代码实现

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

    def InsertInHead(self, val_list):
        """
        头插法
        :param val_list:
        :return:
        """
        prehead = self.__head
        for val in val_list:
            new_node = DoubleLinkNode(val)
            if self.IsEmpty():
                prehead.next = new_node
                new_node.prior = prehead
            else:
                new_node.next = prehead.next
                prehead.next.prior = new_node
                prehead.next = new_node
                new_node.prior = prehead

    def InsertInTail(self, val_list):
        """
        尾插法
        :param val_list:
        :return:
        """
        prehead = self.__head
        for val in val_list:
            new_node = DoubleLinkNode(val)
            prehead.next = new_node
            new_node.prior = prehead
            prehead = prehead.next

    def IsEmpty(self):
        """
        判断双链表是否为空, 空表返回True
        :return:
        """
        if self.__head.next is None:
            return True

    def LengthList(self):
        """
        返回双链表的长度
        :return:
        """
        prehead = self.__head
        count = 0
        if self.IsEmpty():
            return count
        while prehead.next:
            count += 1
            prehead = prehead.next
        return count

    def TraverseList(self):
        """
        遍历双链表, 并打印
        :return:
        """
        prehead = self.__head
        if self.IsEmpty():
            print('链表为空!')
            return 0
        while prehead.next:
            prehead = prehead.next
            print(prehead.data, end=' ')
        print('')

    def InsertInPosition(self, pos, data):
        """
        在某个位置插入
        :param pos: [1, LengthSingleLinkList + 1]
        :param data:
        :return:
        """
        prehead = self.__head
        new_node = DoubleLinkNode(data)
        if pos <= 0 or pos > self.LengthList() + 1:
            print('插入位置错误!')
            return 0
        count = 0
        while count < pos - 1:
            prehead = prehead.next
            count += 1
        if prehead.next is not None:
            new_node.next = prehead.next
            prehead.next.prior = new_node
        prehead.next = new_node
        new_node.prior = prehead

    def SearchWithPosition(self, pos):
        """
        按位置查找元素
        :param pos: [1, LengthSingleLinkList]
        :return:
        """
        prehead = self.__head
        if pos <= 0 or pos > self.LengthList():
            print('位置错误!')
            return -1
        count = 0
        while count < pos:
            prehead = prehead.next
            count += 1
        data = prehead.data
        return data

    def SearchWithVal(self, data):
        """
        按值查找元素
        :param data:
        :return:
        """
        prehead = self.__head
        count = 0
        while prehead.next:
            prehead = prehead.next
            count += 1
            if prehead.data == data:
                return count
        print('该节点不存在!')
        return -1

    def RemoveWithPosition(self, pos):
        """
        按位置移除元素
        :param pos: [1, LengthSingleLinkList]
        :return:
        """
        prehead = self.__head
        if pos <= 0 or pos > self.LengthList():
            print('位置错误!')
            return 0
        count = 0
        while count < pos - 1:
            prehead = prehead.next
            count += 1
        temp = prehead.next
        if temp.next is None:
            prehead.next = None
        else:
            prehead.next = temp.next
            temp.next.prior = prehead
        del temp

    def RemoveWithVal(self, data):
        """
        按值移除元素
        :param data:
        :return:
        """
        prehead = self.__head
        while prehead.next:
            prehead = prehead.next
            if prehead.data == data:
                if prehead.next is None:
                    prehead.prior.next = None
                else:
                    prehead.prior.next = prehead.next
                    prehead.next.prior = prehead.prior
                return -1
        print('该节点不存在!')

  测试代码如下：

from LinkList import DoubleLinkList


if __name__ == '__main__':
    l1 = DoubleLinkList()
    print('头插法创建双链表l1: ', end='')
    l1.InsertInHead([1, 3, 5, 7])
    l1.TraverseList()

    l2 = DoubleLinkList()
    print('尾插法创建双链表l2: ', end='')
    l2.InsertInTail([1, 3, 5, 7])
    l2.TraverseList()

    print('链表l2的长度为: %d' % l2.LengthList())

    print('在链表l2的第3个位置上插入值为2的节点: ', end='')
    l2.InsertInPosition(3, 2)
    l2.TraverseList()

    print('链表l2的第4个位置上的节点的值为: %d' % l2.SearchWithPosition(4))

    print('链表l2值为7的节点的位置为: %d' % l2.SearchWithVal(7))

    print('移除链表l2的第5个位置上的节点: ', end='')
    l2.RemoveWithPosition(5)
    l2.TraverseList()

    print('移除链表l2值为1的节点: ', end='')
    l2.RemoveWithVal(1)
    l2.TraverseList()

  运行结果如下：