swap-nodes-in-pairs(单链表交换点对)

题目描述

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

For example,
Given1->2->3->4, you should return the list as2->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.

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) {
 *         val = x;
 *         next = null;
 *     }
 * }
 */
public class Solution {
    public ListNode swapPairs(ListNode head) {
        ListNode node = new ListNode(0);
        node.next = head;
        ListNode p = node;
        ListNode tmp;
        while(p.next != null && p.next.next != null) {
            tmp = p.next.next;
            p.next.next = tmp.next;
            tmp.next = p.next;
            p.next = tmp;
            p = tmp.next;
        }
        head = node.next;
        node.next = null;
        return head;
    }
}