Educational Codeforces Round 66 (Rated for Div. 2) B. Catch Overflow!

You are given a function f written in some basic language. The function accepts an integer value, which is immediately written into some variable x. x is an integer variable and can be assigned values from 0 to 232−1. The function contains three types of commands:

for n — for loop;
end — every command between “for n” and corresponding “end” is executed n times;
add — adds 1 to x.
After the execution of these commands, value of x is returned.

Every “for n” is matched with “end”, thus the function is guaranteed to be valid. “for n” can be immediately followed by “end”.“add” command can be outside of any for loops.

Notice that “add” commands might overflow the value of x! It means that the value of x becomes greater than 232−1 after some “add” command.

Now you run f(0) and wonder if the resulting value of x is correct or some overflow made it incorrect.

If overflow happened then output “OVERFLOW!!!”, otherwise print the resulting value of x.

Input
The first line contains a single integer l (1≤l≤105) — the number of lines in the function.

Each of the next l lines contains a single command of one of three types:

for n (1≤n≤100) — for loop;
end — every command between “for n” and corresponding “end” is executed n times;
add — adds 1 to x.
Output
If overflow happened during execution of f(0), then output “OVERFLOW!!!”, otherwise print the resulting value of x.

题意：自定义的for循环加法。
题解：用队列存，注意防爆栈

#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#define PI acos(-1)
#define ll long long
using namespace std;
int n;
int main() {
	ios::sync_with_stdio(false);
	cin.tie(0);
	ll MAX = pow(2,32)-1;
	//cout << MAX << endl;
	ll n, x, ans = 0;
	bool f = false;
	cin >> n;
	stack q;
	q.push(1);
	for (ll i = 0; i < n; i++) {
		string s;
		cin >> s;
		if (s[0] == 'f') {
			cin >> x;
			if (q.top() > MAX)x = 1;
			q.push(x*q.top());
		}
		else if (s[0] == 'e') q.pop();
		else ans += q.top();
		if (ans > MAX) f = true;
		
	}
	if (!f) cout << ans << endl;
	else cout << "OVERFLOW!!!" << endl;
//	system("pause");
	return 0;
}