UVa 11995 I Can Guess the Data Structure! (STL)

/*0.036s*/

#include<cstdio>
#include<queue>
#include<stack>
using namespace std;

const int maxn = 1000 + 10;
int n, t[maxn], v[maxn];

int check_stack()
{
	stack<int> s;
	for (int i = 0; i < n; i++)
	{
		if (t[i] == 2)
		{
			if (s.empty()) return 0;
			int x = s.top();
			s.pop();
			if (x != v[i]) return 0;
		}
		else s.push(v[i]);
	}
	return 1;
}

int check_queue()
{
	queue<int> s;
	for (int i = 0; i < n; i++)
	{
		if (t[i] == 2)
		{
			if (s.empty()) return 0;
			int x = s.front();
			s.pop();
			if (x != v[i]) return 0;
		}
		else s.push(v[i]);
	}
	return 1;
}

int check_pq()
{
	priority_queue<int> s;
	for (int i = 0; i < n; i++)
	{
		if (t[i] == 2)
		{
			if (s.empty()) return 0;
			int x = s.top();
			s.pop();
			if (x != v[i]) return 0;
		}
		else s.push(v[i]);
	}
	return 1;
}

int main()
{
	while (~scanf("%d", &n))
	{
		for (int i = 0; i < n; i++) scanf("%d%d", &t[i], &v[i]);
		int s = check_stack();
		int q = check_queue();
		int pq = check_pq();
		if (!s && !q && !pq) printf("impossible\n");
		else if (s && !q && !pq) printf("stack\n");
		else if (!s && q && !pq) printf("queue\n");
		else if (!s && !q && pq) printf("priority queue\n");
		else printf("not sure\n");
	}
	return 0;
}