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
     */
  
  //使用栈反转链表
    public ListNode ReverseList (ListNode head) {
        if(head==null){
            return null;
        }
        Stack<ListNode> stack=new Stack<>();
        while(head!=null){
            stack.push(head);
            head=head.next;
        }
        ListNode list=stack.pop();
        ListNode node=list;
        while(!stack.isEmpty()){
            list.next=stack.pop();
            list=list.next;
        }
        list.next=null;
        return node;
    }
}