题目描述

模拟栈

JAVA 代码

import java.util.*;
import java.io.*;

class Main{
    static final int N = 100010;
    static int[] stk = new int[N];
    static int tt = 0;

    public static void main(String args[])throws IOException{
        BufferedReader in = new BufferedReader(new InputStreamReader(System.in));
        int m = Integer.parseInt(in.readLine());

        while(m-->0){
            String[] s = in.readLine().split(" ");
            String c = s[0];
            if(c.equals("push")){
                int x = Integer.parseInt(s[1]);
                //尾指针 先自增 再入栈
                stk[++tt] = x;
            }else if(c.equals("pop")){
                //尾指针自减
                tt--;
            }else if(c.equals("query")){
                //栈顶为 尾指针的值.
                System.out.println(stk[tt]);
            }else{
                //尾指针不为0 则不为空
                if(tt>0) System.out.println("NO");
                else System.out.println("YES");
            }
        }

    }
}