交换链表的相邻的节点

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.

交换链表的相邻的节点

原文：http://www.cnblogs.com/yangscode/p/5030696.html