Swap Nodes in Pairs

[LeetCode]

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

Total Accepted: 95332 Total Submissions: 270806 Difficulty: Easy

Question

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.

Ways

最讨厌的就是这种指针来回走的题！

先是自己定义了一个头部，然后first指向这个头部answer，然后next指向链表的第一个元素。因为要把前两个元素翻转，所以用after保存第三个元素。

然后就是一系列翻转，我老是搞错。。好囧。

/**

 * Definition for singly-linked list.

 * public class ListNode {

 *     int val;

 *     ListNode next;

 *     ListNode(int x) { val = x; }

 * }

 */

public class Solution {

    public ListNode swapPairs(ListNode head) {

        if(head==null || head.next==null){

            return head;

        }

        ListNode answer=new ListNode(0);

        answer.next=head;

        ListNode first=answer;

        ListNode next=answer.next;

        ListNode after;

        while(next!=null && next.next!=null){

            after=next.next.next;

            next.next.next=next;

            first.next=next.next;

            next.next=after;

            first=next;

            next=after;

        }

        return answer.next;

    }

}

AC:1ms

Date

2016/5/1 20:24:22

巴特西

【LeetCode】Swap Nodes in Pairs 解题报告

Swap Nodes in Pairs

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