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]

示例 2：

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

题解

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode() {}
 *     ListNode(int val) { this.val = val; }
 *     ListNode(int val, ListNode next) { this.val = val; this.next = next; }
 * }
 */
class Solution {
    public ListNode reverseBetween(ListNode head, int left, int right) {
        //在链表之前申请一个结点
        ListNode dummy = new ListNode(0,head), p0 = dummy;
        //将p0定位到left钱一个结点
        for (int i = 0; i < left - 1; i++) {
            p0 = p0.next;
        }
        //反转left到right之间的链表
        ListNode pre = null;
        ListNode cur = p0.next;
        for (int i = 0; i < right - left + 1; i++) {
            ListNode nxt = cur.next;
            cur.next = pre;
            pre = cur;
            cur = nxt;
        }
        //将例子中的1指向4 2指向5
        p0.next.next = cur;
        p0.next = pre;
        return dummy.next;
    }
}