LeetCode 25. A set of K flipped linked lists

原题网址：https://leetcode.cn/problems/reverse-nodes-in-k-group/submissions/

给一个链表,一个k值,要求每k个节点为一组,进行翻转,不足k的不用管;

    // 每knodes are a set of,Flip the nodes of this group.
    // 如果不够k个,就不用翻转了.
	public ListNode reverseKGroup(ListNode head, int k) {
    

		// A virtual node needs to be set up
		ListNode dummyHead = new ListNode(-1);
        dummyHead.next = head;
		ListNode node = dummyHead;

        ListNode frist = head;
        ListNode tail = head;
        ListNode cur = head;

	
		while(cur != null) {
    


            for(int i=0;i<k-1;i++) {
    
                tail = tail.next;
                if(tail == null) {
    
                    return dummyHead.next;
                }
            }

            // 截取k个节点,断开
            ListNode next = tail.next;
            tail.next = null;
            node.next = null;

            // 翻转
            ListNode result = reverseList(frist);

            frist.next= next;
            node.next = tail;


            node = frist;
            cur = next;
            frist = cur;
            tail = cur;
		}
		return dummyHead.next;



	}

	private ListNode reverseList(ListNode head) {
    

		ListNode first= null;

		ListNode cur = head;
		while(cur != null) {
    
			ListNode next = cur.next;
			cur.next = first;
			first = cur;

			cur = next;
		}
		return first;

	}