【LeetCode with Python】 Swap Nodes in Pairs

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原题页面：https://oj.leetcode.com/problems/swap-nodes-in-pairs/

题目类型：链表

难度评价：★

本文地址：/article/1377557.html

Given a linked list, swap every two adjacent nodes and return its head.

For example,

Given

1->2->3->4

, you should return the list as

2->1->4->3

.

Your algorithm should use only constant space. You may not modify the values in the list, only nodes itself can be changed.

交换单链表中每一对相邻的奇偶数下标的元素，注意防止链表长度可能是奇数，即不要忘记检查second_node是否为None。

class Solution:
    # @param a ListNode
    # @return a ListNode
    def swapPairs(self, head):
        if None == head:
            return head
        new_head = ListNode(0)
        new_head.next = head
        last_node = new_head
        while True:
            first_node = last_node.next
            if None == first_node:
                break
            second_node = first_node.next
            if None == second_node:
                break
            last_node.next = second_node
            first_node.next = second_node.next
            second_node.next = first_node
            last_node = first_node
        return new_head.next