Given a linked list and two values v1 and v2. Swap the two nodes in the linked list with values v1 and v2. It‘s guaranteed there is no duplicate values in the linked list. If v1 or v2 does not exist in the given linked list, do nothing.
Notice
You should swap the two nodes with values v1 and v2. Do not directly swap the values of the two nodes.
Example
Given 1->2->3->4->null and v1 = 2, v2 = 4.
Return 1->4->3->2->null.
[LintCode] Swap Two Nodes in Linked List 交换链表中的两个结点
原文：http://www.cnblogs.com/grandyang/p/5493999.html