[数据结构与算法]leetcode-24-两两交换链表中的节点

1.问题描述
https://leetcode-cn.com/problems/swap-nodes-in-pairs/comments/

2.解题代码

/*
 * @lc app=leetcode.cn id=24 lang=csharp
 *
 * [24] 两两交换链表中的节点
 */

// @lc code=start
/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     public int val;
 *     public ListNode next;
 *     public ListNode(int val=0, ListNode next=null) {
 *         this.val = val;
 *         this.next = next;
 *     }
 * }
 */
public class Solution {
    public ListNode SwapPairs(ListNode head) {
        if (head == null)
        {
            return head;
        }

        ListNode node_1 = head;
        ListNode node_2 = head.next;

        ListNode nodeReturn = node_2 == null ? node_1 : node_2;

        ListNode nodeSecond = null;
        while (node_1 != null && node_2 != null)
        {
            ListNode listNextNode = node_2.next;

            node_1.next = node_2.next;
            node_2.next = node_1;

            if (nodeSecond != null)
            {
                nodeSecond.next = node_2;
            }

            if (listNextNode == null || listNextNode.next == null)
            {
                break;
            }
            nodeSecond = node_1;
            node_1 = listNextNode;
            node_2 = listNextNode.next;
        }
        return nodeReturn;
    }
}
// @lc code=end