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;


    }
};