题目：
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.
我的解法：（１）算法思想：
顺序遍历一次链表即可，成对交换结点的值。
（２）代码如下：
原文：http://blog.csdn.net/littlebob180/article/details/43273591