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(head==null){
            return head;
        }
        ListNode headFirst=new ListNode(-1);
        headFirst.next=head;
        ListNode left=head;
        ListNode pre=headFirst;
        for(int i=1;i<m;i++){
            left=head.next;
            pre=pre.next;
            head=head.next;
        }
        ListNode right=left;
        ListNode cur=left;
        ListNode headB=null;
        for(int j=m;j<=n;j++){
            ListNode nextB=cur.next;
            cur.next=headB;
            headB=cur;
            cur=nextB;
        }
        pre.next=headB;
        right.next=cur;
        return headFirst.next;
    }
}