题目

给你单链表的头指针 head 和两个整数 left 和 right ，其中 left <= right 。请你反转从位置 left 到位置 right 的链表节点，返回 反转后的链表 。

示例 1：

输入：head = [1,2,3,4,5], left = 2, right = 4
输出：[1,4,3,2,5]

解

class Solution {public ListNode reverseBetween(ListNode head, int left, int right) {if (head == null || head.next == null) {return head;}ListNode dummy = new ListNode(0);dummy.next = head;int count = 0;ListNode p1 = dummy;ListNode cur = head;ListNode next = null;while (cur != null) {next = cur.next;count++;if (count == left - 1) {p1 = cur;} else if (count == right) {ListNode p2 = p1.next;cur.next = null;p1.next = null;reverse(p2);p2.next = next;p1.next = cur;break;}cur = next;}return dummy.next;}private void reverse(ListNode head){if (head == null || head.next == null) {return;}ListNode pre = null;ListNode cur = head;ListNode next = null;while(cur != null){next = cur.next;cur.next = pre;pre = cur;cur = next;}}
}