【LeetCode】Swap Nodes in Pairs 解题报告
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