题目链接：http://uva.onlinejudge.org/index.php?option=com_onlinejudge&Itemid=8&page=show_problem&category=&problem=3146&mosmsg=Submission+received+with+ID+14262472

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

题目意思很简单，思路也很简单，直接模拟判断就是啦。。。。。

code：

#include<cstdio>
#include<cstring>
#include<iostream>
#include<algorithm>
#include<cmath>
#include<stack>
#include<queue>

using namespace std;

const int maxn=1010;

int a[maxn],b[maxn];
int n;

bool fs()
{
    stack<int > s;
    for(int i=1;i<=n;i++)
    {
        if(a[i]==1)
        {
            s.push(b[i]);
        }
        else
        {

            if(s.empty()) return false;
            int d=s.top();
            if(d!=b[i])
            {
                return false;
            }
            else
            {
                s.pop();
            }
        }
    }
    return true;
}
bool fq()
{
    queue<int > q;
    for(int i=1;i<=n;i++)
    {
        if(a[i]==1)
        {
            q.push(b[i]);
        }
        else
        {

            if(q.empty()) return false;
            int d=q.front();
            if(d!=b[i])
            {
                return false;
            }
            else
            {
                q.pop();
            }
        }
    }
    return true;
}

bool fQ()
{
    priority_queue<int,vector<int>,less<int> >Q;
    for(int i=1;i<=n;i++)
    {
        if(a[i]==1)
        {
            Q.push(b[i]);
        }
        else
        {

            if(Q.empty()) return false;
            int d=Q.top();
            if(d!=b[i])
            {
                return false;
            }
            else
            {
                Q.pop();
            }
        }
    }
    return true;

}

int main()
{
    while(scanf("%d",&n)==1)
    {
        for(int i=1;i<=n;i++)
        {
            scanf("%d%d",&a[i],&b[i]);
        }
        bool flag1=fs(),flag2=fq(),flag3=fQ();
        if(flag1==false&&flag2==false&&flag3==false)
        {
            printf("impossible\n");
        }
        else if(flag1==true&&flag2==false&&flag3==false)
        {
            printf("stack\n");
        }
        else if(flag1==false&&flag2==true&&flag3==false)
        {
            printf("queue\n");
        }
        else if(flag1==false&&flag2==false&&flag3==true)
        {
            printf("priority queue\n");
        }
        else
        {
            printf("not sure\n");
        }
    }
    return 0;
}

uva 11995 - I Can Guess the Data Structure!