Translation of title

Guess the data structure

Question Description:

You have a data structure similar to a "package" that supports two operations, as shown in the table below. 1x: Put element x into package 2: Take an element out of package and give a series of operations and return values. Your task is to guess what the "package" is. It could be a stack < FIFO), a queue (FIFO), a priority queue (large integer FIFO) or something weird.

Input:

The first action is an integer n (1 < n < 1 000). The following N lines are either a type 1 command or a type 2 command followed by an integer x(1 < x < 100). This integer x means that after executing the command of type 2, the package returns x without error. The size of the input file does not exceed 1MB.

Output:

Output a line. There are five possible outputs.

Stack: It must be a stack

Queue: It must be a queue

Priority queue: must be a priority queue

impossible: Must not be the three above

not sure: At least two are possible.

Input examples:

5 1 5 1 3 1 2 2 2 2 3

Output example:

stack

Title Description

PDF

Input and Output Format

Input format:

 

 

Output format:

 

 

Input and Output Samples

Input sample #1:copy

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 sample #1:copy

queue
not sure
impossible
stack
priority queue

Analysis:

Simple simulation will do.

#include<vector>
#include<cstdio>
#include<stack>
#include<queue>
using namespace std;
 
struct Data_Struct
{
    //vc store instruction pair sequence
    vector<pair<int,int> > vc;
 
    //Constructor
    Data_Struct(int n)
    {
        for(int i=0;i<n;i++)
        {
            int x,y;
            scanf("%d%d",&x,&y);
            vc.push_back(make_pair(x,y));
        }
    }
 
    //Determine whether it might be a stack
    bool is_stack()
    {
        stack<int> S;
        for(int i=0;i<vc.size();i++)
        {
            int x=vc[i].first, y=vc[i].second;
            if(x==1) S.push(y);
            else if(x==2)
            {
                if(S.empty() || S.top()!=y ) return false;
                S.pop();
            }
        }
        return true;
    }
 
    //Determine whether it might be a queue
    bool is_queue()
    {
        queue<int> Q;
        for(int i=0;i<vc.size();i++)
        {
            int x=vc[i].first, y=vc[i].second;
            if(x==1) Q.push(y);
            else if(x==2)
            {
                if(Q.empty() || Q.front()!=y ) return false;
                Q.pop();
            }
        }
        return true;
    }
 
    //Determine whether a priority queue is possible
    bool is_priority_queue()
    {
        priority_queue<int> Q;
        for(int i=0;i<vc.size();i++)
        {
            int x=vc[i].first,y=vc[i].second;
            if(x==1) Q.push(y);
            else
            {
                if(Q.empty() || Q.top()!=y )return false;
                Q.pop();
            }
        }
        return true;
    }
 
    //Output integration results
    void solve()
    {
        int S=is_stack(), Q=is_queue(), PQ=is_priority_queue();
 
        if(S+Q+PQ==0) printf("impossible\n");
        else if(S+Q+PQ==1)
        {
            if(S) printf("stack\n");
            else if(Q) printf("queue\n");
            else if(PQ) printf("priority queue\n");
        }
        else if(S+Q+PQ>1)
            printf("not sure\n");
    }
};
 
int main()
{
    int n;
    while(scanf("%d",&n)==1)
    {
        Data_Struct ds(n);
 
        ds.solve();
    }
    return 0;
}