题目描述

输入样例

10
push 6
empty
query
pop
empty
push 3
push 4
pop
query
push 6

输出样例

NO
6
YES
4

参考代码

#include <iostream>

using namespace std;

const int N = 100010;

int q[N], hh, tt;

int m, x;
string op;

void init()
{
    hh = 0;
    tt = -1;
}

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

void pop()
{
    hh++;
}

string empty()
{
    return tt < hh ? "Yes" : "No";
}

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

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