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
        Stack<ListNode> objects = new Stack<>();
        while(head != null){
            objects.push(head);
            head = head.next;
        }

        if(objects.size() == 0){
            return null;
        }else {
            ListNode last = objects.pop();
            ListNode last2 = last;
            while(!objects.isEmpty()){
                ListNode next = objects.pop();
                last2.next = next;
                last2 = last2.next;
            }
            last2.next = null;
            return last;
        }
    }
}