leetcode—Swap Nodes in Pairs

1.题目描述

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.

2.解法分析

/**

 * 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) {

        // Start typing your C/C++ solution below

        // DO NOT write int main() function

        if(head==NULL)return NULL;

        ListNode *cur=head;

        //增加一个头结点有利于是代码整齐

        ListNode* myHead=new ListNode(-1);

        ListNode* prev=myHead;

        prev->next=cur;

        while(cur!=NULL&&cur->next!=NULL)

        {

            prev->next=cur->next;

            cur->next=cur->next->next;

            prev->next->next=cur;

            prev=cur;

            cur=cur->next;

        }

        prev=myHead->next;

        delete myHead;

        return prev;

    }

};