acwing828.模拟栈

#include <iostream>
using namespace std;
const int N = 100010;
int stk[N],idx,tt = 0;//从0开始，到0时显示栈空
void push(int x){
    stk[++ tt] = x;
}
void pop(){
    --tt;
}
int empty(){
    if(tt==0) return 1;
    else return 0;
}
int query(){
    return stk[tt];
}
int main(){
    int m;
    cin >> m;
    while(m--){
        string op;
        cin >> op;
        if(op == "push"){
            int x;
            cin >> x;
            push(x);
        }else if(op == "pop"){
            pop();
        }else if(op == "empty"){
            if(empty()) cout << "YES" << endl;
            else cout << "NO" << endl;
        }else{
            cout << query() << endl;
        }
    }
    return 0 ;
}