[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;
    }
};