24. Swap Nodes in Pairs

题目

Given a linked list, swap every two adjacent nodes and return its head.

You may not modify the values in the list's nodes, only nodes itself may be changed.

Example:

Given 1->2->3->4, you should return the list as 2->1->4->3.

题目大意

两两相邻的元素，翻转链表

解题思路

按照题意做即可。