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;
}