栈与乘积 / 栈

题目

代码

#include 
using namespace std;
using ll = long long;

const int N = 1e5+10;

struct node
{
	int w, pos;
};

node stk[N];
int p, cnt;
int stk0[N], p0;

int main()
{
	int n;
	cin >> n;
	
	while(n--)
	{
			int op;
			cin >> op;
			if(op == 1)
			{
				int x;
				cin >> x;
				if(x == 1)
				{
					cnt++;
					continue;
				}
				stk[++p] = {x, ++cnt};
				if(x == 0) stk0[++p0] = cnt;
			}
			else if(op == 2)
			{
				if(cnt) cnt--;
				if(stk[p].pos > cnt)
				{
					int x = stk[p--].w;
					if(x == 0) p0--;
					
				}
			}
			else if(op == 3)
			{
				int x;
				cin >> x;
				if(cnt < x) puts("ERROR");
				else if(stk0[p0] >= cnt - x + 1) puts("0");
				else
				{
					ll t = 1;
					for(int i = p; stk[i].pos >= cnt - x + 1; i--)
					{
						t *= stk[i].w;
						if(t >= (1ll << 32)) break;
					}
					
					if(t >= (1ll << 32)) puts("OVERFLOW");
					else cout << t << '\n';
				}
			}
	}

}