题解 | 链表中的节点每k个一组翻转

import java.util.*;

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

public class Solution {
    /**
     * 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
     *
     *
     * @param head ListNode类
     * @param k int整型
     * @return ListNode类
     */
    public ListNode reverseKGroup (ListNode head, int k) {
        ListNode res = new ListNode(0);
        ListNode resR = res;
        ListNode r = head;
        ListNode h = head;
        for (int i = 1; head != null; i += k) {
            int j = 1;
            for (j = 1; head != null && j <= k; j++) {
                r = head;
                head = head.next;
            }
            r.next = null;
            if(j < k+1) {
                resR.next = h;
                break;
            }

            ListNode tmp = reverseList(h);//h~r
            resR.next = tmp;

            while (resR.next != null) {
                resR = resR.next;
            }

            h = head;
        }
        return res.next;
    }

    public ListNode reverseList(ListNode head) {
        ListNode res = new ListNode(0);
        ListNode tmp = head;
        while (head != null) {
            head = head.next;
            tmp.next = res.next;
            res.next = tmp;
            tmp = head;
        }
        return res.next;
    }
}