题解 | #反转链表#

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 
     * @return ListNode类
     */
    public ListNode ReverseList (ListNode head) {
        if(head == null) return head;
        // write code here
        ListNode next = head.next;
        if(next == null){
            return head;
        }else{
            head.next = null;
            ListNode newHead = this.ReverseList(next);
            next.next = head;
            return newHead;
        }
    }
}