leetcode-24. Swap Nodes in Pairs

leetcode-24. Swap Nodes in Pairs

题目：

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.

感觉没什么要说的，，都是常规思路，链表加哑节点，然后循环条件判断是否为空，剩下的就是指针互相指了。细心一点就好

/**
 * 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) {
        ListNode dump = new ListNode(0);
        ListNode ret = dump;
        dump.next = head;
        while(dump.next != null && dump.next.next != null){
            ListNode tmp = dump.next;
            dump.next = tmp.next;
            tmp.next = dump.next.next;
            dump.next.next = tmp;
            dump = dump.next.next;
        }
        return ret.next;
    }
}