题解 | #链表内指定区间反转#

import java.util.*;

/*
 * public class ListNode {
 *   int val;
 *   ListNode next = null;
 *   public ListNode(int val) {
 *     this.val = val;
 *   }
 * }
 */

public class Solution {
    /**
     * 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
     *
     *
     * @param head ListNode类
     * @param m int整型
     * @param n int整型
     * @return ListNode类
     */
    public ListNode reverseBetween (ListNode head, int m, int n) {
        ListNode dummyNode = new ListNode(-1);
        dummyNode.next = head;
        ListNode pre = dummyNode;
        for (int i = 0; i < m - 1; i++) {
            pre = pre.next;
        }

        ListNode rightNode = pre;
        for (int i = 0; i < n - m + 1; i++) {
            rightNode = rightNode.next;
        }

        ListNode leftNode = pre.next;
        ListNode cur = rightNode.next;

        pre.next = null;
        rightNode.next = null;

        reverseLinkedList(leftNode);
        pre.next = rightNode;
        leftNode.next=cur;
        return dummyNode.next;
    }

    private void reverseLinkedList(ListNode head) {
        ListNode pre = null;
        ListNode cur = head;
        while (cur != null) {
            ListNode cur_next = cur.next;
            cur.next = pre;
            pre = cur;
            cur = cur_next;
        }
    }
}

思路和BM1是差不多的，不过多了前期准备。

先将链表进行分割，进行反转后拼接