leetcode: swap-nodes-in-pairs

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.

解题思路：

1. 首先理解题意，将链表成对成对的反转，如果是单数的话，末尾节点不做处理
2. 我们首先处理处理掉空链表和单链表的情况
3. 这道题考察的核心是反转链表，只不过反转的是长度是间隔两个
4. 建议画图配合理解

代码如下:

    public ListNode swapPairs(ListNode head) {
        if(head == null || head.next == null) return head;

        ListNode dummy = new ListNode(-1);
        dummy.next = head;
        ListNode start = dummy;

        ListNode p = null;
        ListNode temp = null;

	
        while(start.next != null && start.next.next != null){
            p = start.next;
            temp =p.next;
            p.next = temp.next;
            temp.next = start.next;
            start.next = temp;
            start = p;
        }
        return dummy.next;
    }

转载于:https://my.oschina.net/happywe/blog/3084930