LeetCode#24 Swap Nodes in Pairs
Problem Definition:
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.
Solution: 题目要求不能直接交换链表结点的元素值。（虽然跑起来OJ也发现不了）
用递归实现起来是比较简单直观的，无需构造首节点什么的。这里要注意处理奇数个节点的情况。
1 # @param {ListNode} head 2 # @return {ListNode} 3 def swapPairs(self, head): 4 return self.recur(head, head.next) if head else None 5 6 def recur(self, p, q): 7 if q==None: 8 return p 9 tmp=q.next 10 q.next=p 11 p.next=self.recur(tmp, tmp.next) if tmp else None 12 return q
