题解 | #【模板】栈#

using System.Collections.Generic;
using System;
public class Program {
    public static void Main() {
        Stack stack = new Stack();
        //先读取第一行的个数
        int n = int.Parse(System.Console.ReadLine());
        while( n-- > 0 ){
            //读取操作
            string opr = System.Console.ReadLine ();
            if(opr.IndexOf("push")!=-1){
                string[] strs = opr.Split(" ");
                stack.Push(int.Parse(strs[1]));
            }else if(opr.Equals("pop")){
                stack.Pop();
            }else if(opr.Equals("top")){
                stack.Peek();
            }
        }
    }
}
public class Stack{
    List<int> nums = new List<int>();
    public void Push(int val){
        nums.Add(val);
    }
    public void Pop(){
        if(nums.Count == 0){
            Console.WriteLine("error");
            return;
        }
        Console.WriteLine(nums[nums.Count-1]);
        nums.RemoveAt(nums.Count-1);
    }

    public void Peek(){
        if(nums.Count == 0){
            Console.WriteLine("error");
            return ;
        }
        Console.WriteLine(nums[nums.Count-1]);
    }
}