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). 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.
每一行输入两个数，第一个数若是1，则表示输入第二个数，若第一个数是2，则表示输出第二个数，判断这是什么结构
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

#include <iostream>#include <cstring>#include <queue>#include <stack>#include <algorithm>#include <cstdio>using namespace std;int main(){int n;int f1,f2,f3;while(scanf("%d",&n)!=EOF){stack<int>S;        queue<int>Q;        priority_queue<int>PQ;        f1=1,f2=1,f3=1;for(int i=1;i<=n;i++){int a,b;scanf("%d%d",&a,&b);if(a==1){            S.push(b);          Q.push(b);          PQ.push(b);}else if(!Q.empty()){if(f1&&S.top()!=b)f1=0;S.pop();if(f2&&Q.front()!=b)f2=0;Q.pop();if(f3&&PQ.top()!=b)f3=0;PQ.pop();}else f1=f2=f3=0;}int temp=f1+f2+f3;if(temp==0)printf("impossible\n");else if(temp==1){if(f1)printf("stack\n");else if(f2)printf("queue\n");else printf("priority queue\n");}else printf("not sure\n");}return 0;}