题目描述

输入样例

10
push 5
query
push 6
pop
query
pop
empty
push 4
query
empty

输出样例

5
5
YES
4
NO

参考代码

#include <iostream>

using namespace std;

const int N = 1000010;

int m, x;
int q[N];
string op;
int top;

void init()
{
    top = 0;
}

void push(int x)
{
    q[++top] = x;
}

void pop()
{
    top--;
}

string empty()
{
   if (top == 0) return "Yes";
   return "No";
}


int query()
{
   return q[top]; 
}

int main()
{
    init();
    
    cin >> m;
    while (m--)
    {
        cin >> op;
        if (op == "push")
        {
            cin >> x;
            push(x);
        }
        else if (op == "pop")
        {
            pop();
        }
        else if (op == "query")
        {
            cout << query() << endl;
        }
        else
        {
            cout << empty() << endl;
        }
    }
    return 0;
}