题解 | 两两交换链表中的结点

import java.util.*;

/*
 * public class ListNode {
 *   int val;
 *   ListNode next = null;
 *   public ListNode(int val) {
 *     this.val = val;
 *   }
 * }
 */
//一言难尽，没说链表是奇数还是偶数，默认了偶数，没说是不是非空，默认了非空，好嘛硬是卡了三遍
public class Solution {
    public ListNode swapPairs (ListNode head) {
        int temp1 = 0;
        ListNode res = head;
        if(res==null)return null;
        else if(res.next==null)return head;
        while(head.next!=null&&head.next.next!=null){
            temp1 = head.val;
            head.val = head.next.val;
            head.next.val = temp1;
            head = head.next.next;
        }
        if(head.next!=null){
        temp1 = head.val;
        head.val = head.next.val;
        head.next.val = temp1;
        }
        return res;
    }
}