451. Swap Nodes in Pairs【LintCode java】

Description

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.

解题：将链表中的结点换一下位置。代码如下：

/**
 * Definition for ListNode
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) {
 *         val = x;
 *         next = null;
 *     }
 * }
 */
 
public class Solution {
    /**
     * @param head: a ListNode
     * @return: a ListNode
     */
    public ListNode swapPairs(ListNode head) {
        // write your code here
        ListNode dummy = new ListNode(-1);
        dummy.next = head;
        ListNode pre = dummy;
        while(pre.next != null && pre.next.next != null){
            ListNode t = pre.next.next;
            pre.next.next = t.next;
            t.next = pre.next;
            pre.next = t;
            pre = t.next;
        }
        return dummy.next;
    }
}