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 class Solution {
    /**
     * 
     * @param head ListNode类 
     * @param k int整型 
     * @return ListNode类
     */
    public ListNode reverseKGroup (ListNode head, int k) {

        if (head == null || k < 0) {
            return head;
        }

        int len = 0;
        ListNode temp = head;

        while (temp != null) {
            len++;
            temp = temp.next;
        }

        ListNode headNode = new ListNode(-1);
        headNode.next = head;
        ListNode tempHeadNode = headNode;
        ListNode curNode = head;
        ListNode nextNode = null;

        for (int i = 0; i < len/k; i++) {

            for (int j = 1; j < k; j++) {
                nextNode = curNode.next;
                curNode.next = nextNode.next;
                nextNode.next = tempHeadNode.next;
                tempHeadNode.next = nextNode;
            }

            tempHeadNode = curNode;
            //这样写 也可以curNode = headTempNode.next;
            curNode = curNode.next;

        }

        return headNode.next;
    }
}