92. 反转链表 II(Reverse Linked List II)

来源

来源：力扣（LeetCode）
链接：https://leetcode-cn.com/problems/reverse-linked-list-ii/

描述

反转从位置 m 到 n 的链表。请使用一趟扫描完成反转。
说明:
1 ≤ m ≤ n ≤ 链表长度。

示例:
输入: 1->2->3->4->5->NULL, m = 2, n = 4
输出: 1->4->3->2->5->NULL

题解

使用了四个指针，请君慢慢咀嚼~

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) { val = x; }
 * }
 */
class Solution {
    public ListNode reverseBetween(ListNode head, int m, int n) {
        if (null == head) return null;
        ListNode cur = head, prev = null;
        while (m > 1) {
            prev = cur;
            cur = cur.next;
            m--;
            n--;
        }
        ListNode con = prev, tail = cur;
        ListNode third = null;
        while (n > 0) {
            third = cur.next;
            cur.next = prev;
            prev = cur;
            cur = third;
            n--;
        }
        if (con != null) {
            con.next = prev;
        } else {
            head = prev;
        }
        tail.next = cur;
        return head;
    }
}

复杂度分析

• 时间复杂度:
• 空间复杂度: