【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：http://blog.csdn.net/nerv3x3/article/details/3465506

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