leetcode 25. K 个一组翻转链表（java）

感谢腌菜读作梦想 

反转链表部分的题解写的非常好

芜湖～～～ 

class Solution {
    public ListNode reverseKGroup(ListNode head, int k) {
        ListNode dummy = new ListNode(-1, head);
        ListNode pre = dummy;
        ListNode end = dummy;

        while (end != null) {
            for (int i = 0; i < k && end != null; i++) {
                end = end.next;
            }

            if (end == null) {
                break;
            }

            ListNode start = pre.next;
            ListNode next = end.next;

            end.next = null;
            reverse(start);
            pre.next = end;
            start.next = next;
            pre = start;
            end = start;

        }

        return dummy.next;
    }



    public ListNode reverse(ListNode head) {
        ListNode cur = head;
        ListNode end = null;

        while (cur != null) {
            ListNode tmp = cur.next;
            cur.next = end;
            end = cur;
            cur = tmp;
        }
        return end;
    }
}