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) {
        // write code here
        return reverseListInt(head, null);
    }

    private ListNode reverseListInt(ListNode head, ListNode newHead) {
        if (head == null) {
            return newHead;
        }
        ListNode next = head.next;
        head.next = newHead;
        return reverseListInt(next, head);
    }

}