C++ 代码
#include <iostream>
using namespace std;
const int N = 1e5 + 10;
int e[N], idx = 0;
int m;
string s;
void push(int x)
{
e[idx ++] = x;
}
void empty()
{
if(idx == 0) cout << "YES" << endl;
else cout << "NO" << endl;
}
int main()
{
cin >> m;
while(m --)
{
cin >> s;
if(s[0] == 'p' && s[1] == 'u')
{
int x;
cin >> x;
push(x);
}
else if(s[0] == 'p') idx --;
else if(s[0] == 'q') cout << e[idx - 1] << endl;
else empty();
}
return 0;
}