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) {
        // write code here
        if(head == null || k==1){
            return head;
        }
        int total = 0;
        ListNode temp = head;
        while(temp !=null  ){
            total++;
            temp = temp.next;
        }
        ListNode dummy = new ListNode(0);
        dummy.next = head;
        ListNode pre = dummy;

        while(total>=k){
            ListNode cur = pre.next;
            ListNode nextn;
            for(int i=1;i<k;i++){
                nextn = cur.next;
                cur.next = nextn.next;
                nextn.next = pre.next;
                pre.next=nextn;
            }
            pre = cur;
            total -=k;
        }
        return dummy.next;



        }
    }