UVA 11995 I Can Guess the Data Structure! Solution

Problem Statement :

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

Solution :

#include <cstdio>
#include <iostream>
#include <stack>
#include <queue>

using namespace std;

int main() {
    int i,j,k,l,n,opt,tmp,temp;
   

    while(scanf("%d",&n) == 1) {
        stack S;
        queue Q;
        priority_queue P;
        bool ss ,qq, pp;

        ss = pp = qq = true;
        while(n--) {
            scanf("%d %d",&opt,&tmp); 

            if(opt == 1) {
                if(ss)
                    S.push(tmp);
                if(qq)
                    Q.push(tmp);
                if(pp)
                    P.push(tmp);
            }
            else if(opt == 2) {
                if(ss) {
                    if(!S.empty() && S.top() == tmp) {
                        S.pop();
                    }
                    else ss = false;
                }
                if(qq) {
                    if(!Q.empty() && Q.front() == tmp) {
                        Q.pop();
                    }
                    else 
                        qq = false;
                }
                if(pp) {
                    if(!P.empty() && P.top() == tmp) {
                        P.pop();
                    }
                    else pp = false;
                }
            }
        }

        if(ss && !pp && !qq)
            printf("stack\n");
        else if(!ss && !pp && qq)
            printf("queue\n");
        else if(!ss && pp && !qq)
            printf("priority queue\n");
        else if(pp || qq || ss)
            printf("not sure\n");
        else
            printf("impossible\n");
    }
    return 0;
}