24. Swap Nodes in Pairs

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.

解题思路

利用递归，可以简洁明了地完成程序。详见程序注释。

总结