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

题意：水。。。

代码：

#include
     
      #include
      
       #include
       
        #include
        
         #include
         
          #include
          
           #include
           
            #include
            
             using namespace std;const int INF=0x3f3f3f3f;#define mem(x,y) memset(x,y,sizeof(x))#define SI(x) scanf("%d",&x)#define SL(x) scanf("%lld",&x)#define PI(x) printf("%d",x)#define PL(x) printf("%lld",x)#define P_ printf(" ")#define T_T while(T--)#define F(i,s,x) for(i=s;i
             

q; priority_queue

sq; stack

S; int a=1,b=1,c=1; int temp=0; while(n--){ SI(t);SI(x); if(temp)continue; if(t==1){ q.push(x); sq.push(x); S.push(x); } else{ if(q.empty())temp=1; if(temp)continue; if(q.front()!=x)a=0; if(sq.top()!=x)b=0; if(S.top()!=x)c=0; q.pop(); sq.pop(); S.pop(); } } if(temp||(a+b+c==0))puts("impossible"); else if(a+b+c>1)puts("not sure"); else if(a)puts("queue"); else if(b)puts("priority queue"); else if(c)puts("stack"); } return 0;}