题解 | #牛群的重新分组#

题目考察的知识点

考察链表的遍历操作

题目解答方法的文字分析

为了方便，先写出链表逆序的函数，随后遍历链表，按照k个一组，对组内的链表进行逆序操作。

本题解析所用的编程语言

使用Java语言解答

完整且正确的编程代码

import java.util.*;

/*
 * public class ListNode {
 *   int val;
 *   ListNode next = null;
 *   public ListNode(int val) {
 *     this.val = val;
 *   }
 * }
 */

public class Solution {

    public ListNode reverseKGroup (ListNode head, int k) {
        ListNode dummy = new ListNode(0); //新建虚拟头节点
        dummy.next = head;

        ListNode prev = dummy;
        ListNode curr = head;

        int count = 0;
        while (curr != null) {
            count++;
            if (count % k == 0) {
                prev = reverse(prev, curr.next);  //逆序
                curr = prev.next;
            } else {
                curr = curr.next;
            }
        }

        return dummy.next;
    }
    
    ListNode reverse(ListNode prev, ListNode end) {
        ListNode curr = prev.next;
        ListNode tail = curr;

        while (curr != end) {
            ListNode temp = curr.next;
            curr.next = prev.next;
            prev.next = curr;
            curr = temp;
        }

        tail.next = end;
        return tail;
    }
}