I Can Guess the Data Structure!

 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 isa stack (Last-In, First-Out), a queue (First-In, First-Out), a priority-queue (Always take out largerelements 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 xis always a positive integer not larger than 100. The input is terminated by end-of-file (EOF).OutputFor 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 mentionedabove.

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

1 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

题意：

输入多组数据，每组有t行，x为1时表示将y放入背包，x为2时表示将y从背包中取出。

由取出的顺序不同判断出是队列（先进先出），栈（先进后出），还是优先队列（每次取出最大的）或者这三者均不是或者两种及以上可能。

#include<stdio.h>
#include<queue>
#include<stack>
using namespace std;
int main()
{
    int t;
    while(~scanf("%d",&t))
    {
        queue<int>q;//定义队列
        stack<int>s;//定义栈
        priority_queue<int>p;//定义优先队列（默认从大到小排序）
        int i,j,f[3],x,y;
        for(i=0; i<3; i++)
            f[i]=1;
        for(i=0; i<t; i++)
        {
            scanf("%d%d",&x,&y);
            if(x==1)
            {
                s.push(y);//入栈
                q.push(y);//入队列
                p.push(y);//入优先队列
            }
            else
            {
                if(!s.empty())
                {
                    if(s.top()!=y)//如果取出的元素不等于栈顶元素
                        f[0]=0;
                    s.pop();//清除元素
                }
                else//当栈为空的时候，就不满足
                    f[0]=0;
                if(!q.empty())
                {
                    if(q.front()!=y)//如果取出的元素不等于队首元素
                        f[1]=0;
                    q.pop();
                }
                else
                    f[1]=0;//当队列为空的时候，就不满足
                if(!p.empty())
                {
                    if(p.top()!=y)//如果取出元素不等于队首（最大）元素
                        f[2]=0;
                    p.pop();
                }
                else
                    f[2]=0;
            }
        }
        int sum=0;
        for(i=0; i<3; i++)
        {
            if(f[i]==1)
                sum++;
        }
        if(sum==0)//如果不满足以上三个条件
            printf("impossible\n");
        else if(sum>1)//当满足多个条件
            printf("not sure\n");
        else//满足一种条件
        {
            if(f[0]==1)
                printf("stack\n");
            else if(f[1]==1)
                printf("queue\n");
            else if(f[2]==1)
                printf("priority queue\n");
        }
    }
    return 0;
}