Leetcode and Lintcode

Swap Nodes in Pairs

Given a linked list, swap every two adjacent nodes and return its head.

Example
Given 1->2->3->4, you should return the list as 2->1->4->3.

Challenge
Your algorithm should use only constant space. You may not modify the values in the list, only nodes itself can be changed.

Solution:

This is an easay question.
If there are more than two nodes behind, exchange the order of the following two nodes,
and then move the http://www.lintcode.com/en/problem/swap-nodes-in-pairs/pointer 2 places.

Leetcode link
Lintcode link

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/*************************************************************************
	> File Name: SwapNodesinPairs.java
	> Author: Yao Zhang 
	> Mail: psyyz10@163.com 
	> Created Time: Wed 18 Nov 23:21:09 2015
 ************************************************************************/

public class SwapNodesinPairs{
	public ListNode swapPairs(ListNode head) {
        // Write your code here
        ListNode dummy = new ListNode(-1);
        dummy.next = head;
        head = dummy;
        
        while (head.next != null && head.next.next != null){
            ListNode temp = head.next;
            head.next = temp.next;
            temp.next = head.next.next;
            head.next.next = temp;
            head = head.next.next;
        }
        
        return dummy.next;
    }
}