Leetcode-Swap Nodes in Pairs

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.

Have you met this question in a real interview?
 
Solution:
 1 /**
 2  * Definition for singly-linked list.
 3  * public class ListNode {
 4  *     int val;
 5  *     ListNode next;
 6  *     ListNode(int x) {
 7  *         val = x;
 8  *         next = null;
 9  *     }
10  * }
11  */
12 public class Solution {
13     public ListNode swapPairs(ListNode head) {
14         if (head==null || head.next==null) return head;
15         ListNode preHead = new ListNode(0);
16         preHead.next = head;
17         ListNode pre = preHead;
18         ListNode cur = head;
19 
20         while (cur!=null && cur.next!=null){
21            ListNode temp = cur.next.next;
22            pre.next = cur.next;
23            cur.next.next = cur;
24            cur.next = temp;
25            pre=cur;
26            cur = cur.next;
27         }
28 
29         return preHead.next;
30     }
31 }

 

posted @ 2014-11-21 05:23  LiBlog  阅读(129)  评论(0)  编辑  收藏  举报