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) {
        if(m==n)return head;
       
       ListNode p = head;
       for(int i = 1;i<m;i++){
           p = p.next;
       }
       ListNode e = head;
        for(int i =1;i<=n;i++){
           e = e.next;
        }
         ListNode pre = null;
        if(e != null){
           pre = e;
        }
        ListNode nx= null;
        for(int i = 0;i <= n-m;i++){
             nx = p.next;
             p.next = pre;
             pre = p;
             p = nx;
        }
        if(m!=1){
          ListNode q = head;
        for(int i = 1;i < m-1;i++){
            q = q.next;
        }
            q.next = pre;
            return head;
        }
        return pre;
        // write code here
    }
}