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) {
        // write code here
        if(m == n)
            return head;

        if(m == 1){
            ListNode L1 = head;
            int mc = m;
            int nc = n;

            while(nc != 1){
                nc--;
                L1 = L1.next;
            }

            ListNode L2 = L1;
            ListNode L3 = L2.next;
            L1 = head;

            L2.next = null;

            ListNode pre = L3;
            ListNode cur = L1;
            
            while(cur != null){
                ListNode temp = cur.next;
                cur.next = pre;
                pre = cur;
                cur = temp;
            }
            return pre;
        }
        else{
            ListNode L1 = head;
            ListNode L2 = head;
            ListNode L3 = head;
            ListNode L4 = head;
            int mc = m;
            int nc = n;

            while(mc != 1){
                mc--;
                L2 = L2.next;
                if(L2 != L1.next){
                    L1 = L1.next;
                }
            }

            while(nc != 1){
                nc--;
                L3 = L3.next;
            }
            L4 = L3.next;

            L3.next = null;
            L1.next = L3;

            ListNode pre = L4;
            ListNode cur = L2;
            

            while(cur != null){
                ListNode temp = cur.next;
                cur.next = pre;
                pre = cur;
                cur = temp;
            }
            return head;
        }
         
    }
}

菜鸟第一次晒屎山代码。还是用了反转列表的思路，但是分了两种情况：

1.从第一个开始转

2.不是从第一个开始转