UVa11995 I Can Guess the Data Structure!

Problem I

I Can Guess the Data Structure!

There is a bag-like data structure, supporting two operations:

1 x

Throw an element x into the bag.

2

Take out an element from the bag.

Given a sequence of operations with return values, you're going to guess the data structure. It is a stack (Last-In, First-Out), a queue (First-In, First-Out), a priority-queue (Always take out larger elements first) or something else that you can hardly imagine!

Input

There are several test cases. Each test case begins with a line containing a single integer n (1<=n<=1000). Each of the next n lines is either a type-1 command, or an integer 2 followed by an integer x. That means after executing a type-2 command, we get an element xwithout error. The value of x is always a positive integer not larger than 100. The input is terminated by end-of-file (EOF). The size of input file does not exceed 1MB.

Output

For each test case, output one of the following:

stack

It's definitely a stack.

queue

It's definitely a queue.

priority queue

It's definitely a priority queue.

impossible

It can't be a stack, a queue or a priority queue.

not sure

It can be more than one of the three data structures mentioned above.

Sample Input

6
1 1
1 2
1 3
2 1
2 2
2 3
6
1 1
1 2
1 3
2 3
2 2
2 1
2
1 1
2 2
4
1 2
1 1
2 1
2 2
7
1 2
1 5
1 1
1 3
2 5
1 4
2 4

Output for the Sample Input

queue
not sure
impossible
stack
priority queue

---

Rujia Liu's Present 3: A Data Structure Contest Celebrating the 100th Anniversary of Tsinghua University
Special Thanks: Yiming Li
Note: Please make sure to test your program with the gift I/O files before submitting!

这题其实也就是一个STL的应用题，对于n行的输入输出，判断是哪种容器符合，是queue/stack/priority queue还是not sure以及impossible。对于这题只要按照各个容器的用法使用，然后判断输入输出是否相符合即可。

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

queue<int>q;
stack<int>s;
priority_queue<int>p;

int main() {
	int Test;
	int order;
	int tmp;
	while (cin >> Test) {
		bool cnt_q = true;
		bool cnt_s = true;
		bool cnt_p = true;
		int cnt = 3;
		for (int i = 0; i < Test; i++) {
			cin >> order >> tmp;
			if (cnt_q) {
				if (order == 1)
					q.push(tmp);
				else if (!q.empty() && q.front() == tmp)
					q.pop();
				else {
					cnt--;
					cnt_q = false;
				}
			}
			if (cnt_s) {
				if (order == 1)
					s.push(tmp);
				else if (!s.empty() && s.top() == tmp)
					s.pop();
				else {
					cnt--;
					cnt_s = false;
				}
			}
			if (cnt_p) {
				if (order == 1)
					p.push(tmp);
				else if (!p.empty() && p.top() == tmp)
					p.pop();
				else {
					cnt--;
					cnt_p = false;
				}
			}
		}
		if (!cnt)
			cout << "impossible" << endl;
		else if (cnt > 1)
			cout << "not sure" << endl;
		else if (cnt_q)
			cout << "queue" << endl;
		else if (cnt_s)
			cout << "stack" << endl;
		else
			cout << "priority queue" << endl;
		while (!q.empty())
			q.pop();
		while (!s.empty())
			s.pop();
		while (!p.empty())
			p.pop();
	}
	return 0;
}