力扣-24题（Java）-链表节点交换

àì夳堔傛蜴生んèń 2022-10-05 11:47 181阅读 0赞

题目链接：[https://leetcode-cn.com/problems/swap-nodes-in-pairs/][https_leetcode-cn.com_problems_swap-nodes-in-pairs]  
题目如下：  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzQwNDY3Njcw_size_16_color_FFFFFF_t_70]  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzQwNDY3Njcw_size_16_color_FFFFFF_t_70 1]  
思路：  
![在这里插入图片描述][20210608220136759.png]

/**
     * Definition for singly-linked list.
     * public class ListNode {
     *     int val;
     *     ListNode next;
     *     ListNode() {}
     *     ListNode(int val) { this.val = val; }
     *     ListNode(int val, ListNode next) { this.val = val; this.next = next; }
     * }
     */
    class Solution {
        
        public ListNode swapPairs(ListNode head) {
        
            //tip:
            //1、当整个操作过程中，头节点会发生变动时，可增加一个虚拟节点
            //2、操作中三个指针普遍适用
            //3、链表按着顺序来，从后往前，确保不会出错
            //4、链表题要画图
            if(head==null||head.next==null) return head;//链表中元素仅有0或1个
    
            ListNode dummyhead=new ListNode(0);
            dummyhead.next=head;
            ListNode p=dummyhead; 
    
            while(p.next!=null&&p.next.next!=null){
        
                ListNode node1=p.next;//链表节点数>=2个
                ListNode node2=p.next.next;
                System.out.println(node1.val);
    
                
                node1.next=node2.next;
                node2.next=node1;
                p.next=node2;
                //dummyhead->node1->node2 before
                //dummyhead->node2->node1 after
    
                p=node1;
            }
            
            return dummyhead.next;
            
        }
    }

[https_leetcode-cn.com_problems_swap-nodes-in-pairs]: https://leetcode-cn.com/problems/swap-nodes-in-pairs/
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzQwNDY3Njcw_size_16_color_FFFFFF_t_70]: /images/20221005/5a8d98fdf084499681941b5022783cbb.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzQwNDY3Njcw_size_16_color_FFFFFF_t_70 1]: /images/20221005/e3e055d3aa924423be69978fa0fa05ad.png
[20210608220136759.png]: /images/20221005/30f3dee2db244accbc45fd44cd417faa.png