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https://leetcode.com/problems/swap-nodes-in-pairs/
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.
题目：将列表中结点两两交换
注意：==的书写和reverse的代码别写错
1 # Definition for singly-linked list.
2 # class ListNode:
3 # def __init__(self, x):
4 # self.val = x
5 # self.next = None
6
7 class Solution:
8 # @param {ListNode} head
9 # @return {ListNode}
10 def swapPairs(self, head):
11 if head==None or head.next==None:
12 return head
13 dummy=ListNode(0)
14 dummy.next=head
15 p=dummy
16 while p.next and p.next.next: #reverse就是将后面的结点依次前置，此处只需前置一项
17 tmp=p.next.next; p.next.next=tmp.next #将前置项删除
18 tmp.next=p.next; p.next=tmp #将前置项前置
19 p=p.next.next
20 return dummy.next
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原文地址：http://www.cnblogs.com/lzsjy421/p/4612374.html
