I Can Guess the Data Structure! uva11995

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). 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

题意：对三种数据结构进行模拟，当编号为1的时候，进栈，进队，进优先对，当为2的时候，就出，判断是否为三种数据结构的某一种或某几种，但是要注意对当前情况的判空

代码：

#include
#include
#include
#include
using namespace std;
int a[1005];
int b[1005];

int main()
{
    int n;
    while(cin>>n)
    {
        int len1 = 0;
        int len2 = 0;
        stack s;
        queue q;
        bool flag1 = true;
        bool flag2 = true;
        bool flag3 = true;
        priority_queue pq;
        for(int i = 0;i>help;
            if(help==1)
            {
                cin>>a[len1];
                s.push(a[len1]);
                q.push(a[len1]);
                pq.push(a[len1]);
                //cout<>b[len2];
                if(!s.empty()&&s.top()!=b[len2]||s.empty())
                    flag1 = false;
                else if(!s.empty()&&s.top()==b[len2])
                    s.pop();

                if(!q.empty()&&q.front()!=b[len2]||q.empty())
                    flag2 = false;
                else if(!q.empty()&&q.front()==b[len2])
                    q.pop();

                if(!pq.empty()&&pq.top()!=b[len2]||pq.empty())
                    flag3 = false;
                else if(!pq.empty()&&pq.top()==b[len2])
                    pq.pop();

                len2++;
            }
        }
        if(len1