LeetCode-024：Swap Nodes in Pairs

题目：

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

Example:

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

Note:

• Your algorithm should use only constant extra space.
• You may not modify the values in the list's nodes, only nodes itself may be changed.

题意：

交换单链表中每对节点的空间！！！

思路：

水题~

Code：

/**
 * 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) {
        ListNode *nhead=new ListNode(0);
        nhead->next=head;
        ListNode *pre=nhead,*cur=head;
        while(cur&&cur->next){
            pre->next=cur->next;
            cur->next=pre->next->next;
            pre->next->next=cur;
            pre=cur;
            cur=cur->next;
        }
        return nhead->next;
    }
};