[leetcode] 24. Swap Nodes in Pairs 解题报告

题目链接：https://leetcode.com/problems/swap-nodes-in-pairs/

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.

思路：这种题比较简单，想清楚他们的链接关系。

/**
* Definition for singly-linked list.
* struct ListNode {
*     int val;
*     ListNode *next;
*     ListNode(int x) : val(x), next(NULL) {}
* };
*/
class Solution {
public:
ListNode* swapPairs(ListNode* head) {
if(!head) return head;
ListNode* pHead = new ListNode(0);
pHead->next = head;
ListNode* p = pHead;
while(p->next && p->next->next)
{
ListNode* q = p->next->next;//链表各种交换，你晕了没^.^
p->next->next = q->next;
q->next = p->next;
p->next = q;
p = p->next->next;
}
head = pHead->next;
delete pHead;
return head;
}
};