UVA - 11995 : 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 x without error. The value of x is always a positive integer not larger than 100. The input is terminated by end-of-file (EOF).
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
Sample Output
queue not sure impossible stack priority queue

给出一些数据放入闭包，根据输出猜测这个闭包是什么数据结构（栈，队列，优先队列，都不是，有两种以上可能）

用三种数据结构分别模拟即可。

Select Code

#include<iostream>
#include<queue>
#include<stack>
#include<string.h>

using namespace std;

int a[1000][2];
int n;

bool checks()
{
	stack<int> s;
	//	cout<<1<<endl;
	for(int i=0;i<1000;i++)
	s.push(0);
	int x;
	for(int i=0;i<n;i++)
	{
		if(a[i][0]==1)
			s.push(a[i][1]);
		if(a[i][0]==2)
		{
			x=s.top();
			s.pop();
			if(x!=a[i][1])
				return false;
		}
	}
	return true;
}

bool checkq()
{
	int x;
//	cout<<1<<endl;
	queue<int> q;

	for(int i=0;i<n;i++)
	{
		if(a[i][0]==1)
			q.push(a[i][1]);
		if(a[i][0]==2)
		{
			if(q.empty())
				return false;
			x=q.front();
		//	cout<<x<<endl;
			q.pop();
			if(x!=a[i][1])
				return false;
		}		
	}
	return true;
}

bool checkp()
{
	int x;
	priority_queue<int> p;
	for(int i=0;i<1000;i++)
		p.push(0);
	for(int i=0;i<n;i++)
	{
		if(a[i][0]==1)
			p.push(a[i][1]);
		if(a[i][0]==2)
		{
			x=p.top();
			p.pop();
			if(x!=a[i][1])
				return false;
		}		
	}
	return true;
}

int main()
{
	while(scanf("%d",&n)!=EOF)
	{
		memset(a,0,sizeof(a));
		for(int i=0;i<n;i++)
			cin>>a[i][0]>>a[i][1];
		bool s=checks();
		bool q=checkq();
		bool p=checkp();
		
		if(s&&!q&&!p)
			cout<<"stack"<<endl;
			else
		if(!s&&q&&!p)
			cout<<"queue"<<endl;
			else
		if(!s&&!q&&p)
			cout<<"priority queue" <<endl;
			else
		if(!s&&!q&&!p)
			cout<<"impossible"<<endl;
			else
		//if(s&&q&&!p||s&&!q&&p||!s&&q&&p||s&&p&&q)
			cout<<"not sure"<<endl;
		
	}
	
	return 0;
}