[UVA] 11995

11995 - I Can Guess the Data Structure!

Time limit: 1.000 seconds

Problem I

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

---

Rujia Liu's Present 3: A Data Structure Contest Celebrating the 100th Anniversary of Tsinghua University
Special Thanks: Yiming Li
Note: Please make sure to test your program with the gift I/O files before submitting!

题解：STL中 queue、stack、priority_queue的使用。

代码：

#include<cstdio>
#include<cstring>
#include<stdbool.h>
#include<cmath>
#include<queue>
#include<stack>
#include<algorithm>


#define rep(i,a,b)      for(i=(a);i<=(b);i++)
#define red(i,a,b)      for(i=(a);i>=(b);i--)
#define clr(x,y)        memset(x,y,sizeof(x))
#define sqr(x)          ((x)*(x))

using namespace std;

int i,j,x,y,pri,qui,sti;
    
void check()
{
    if(qui==1 && pri==0 && sti==0) printf("queue
");
    else
    if(qui==0 && pri==1 && sti==0) printf("priority queue
");
    else
    if(qui==0 && pri==0 && sti==1) printf("stack
");
    else
    if(qui==0 && pri==0 && sti==0) printf("impossible
");
    else
    printf("not sure
");   
}

int main()
{
    int T;
    
   
    
    while(scanf("%d",&T)!=EOF) {
         pri=qui=sti=1;
        
         queue <int> Q;
         stack <int> S;
         priority_queue <int> prQ;
        
        while(T--) {
            scanf("%d%d",&x,&y);
            if(x==1) {
                Q.push(y);
                S.push(y);
                prQ.push(y);
            } 
              else {
               
                  if(qui==1) {
                    if(Q.empty() || Q.front()!=y) qui=0;
                    if(!Q.empty()) Q.pop();
                  }
                   
                  if(sti==1) {
                    if(S.empty() || S.top()!=y) sti=0;
                    if(!S.empty()) S.pop();
                  }   
      
                  if(pri==1) {
                    if(prQ.empty() || prQ.top()!=y) pri=0;
                    if(!prQ.empty()) prQ.pop();
                  }          
             }    
        }
           
            check();
    }
    
    return 0;
}