UVA 11995 I Can Guess the Data Structure!

Description

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

61 11 21 32 12 22 361 11 21 32 32 22 121 12 241 21 12 12 271 21 51 11 32 51 42 4

Output for the Sample Input

queuenot sureimpossiblestackpriority queue

#include<stack>  #include<queue>  using namespace std;  const int maxn = 1000+100;  int id[maxn],x[maxn],n;  bool isStack(){      stack<int> s;      for(int i=0;i<n;i++){          if(id[i]==1) s.push(x[i]);          else{              if(s.empty())  return false;              int val=s.top();  s.pop();              if(x[i]!=val) return false;          }      }      return true;  }  bool isQueue(){  queue<int >q;  for(int i=0;i<n;i++){          if(id[i]==1) q.push(x[i]);          else{              if(q.empty()) return false;              int val=q.front();  q.pop();              if(x[i]!=val) return false;          }      }      return true;  }  bool isPriority(){      priority_queue<int > q;  for(int i=0;i<n;i++){          if(id[i]==1) q.push(x[i]);          else{  if(q.empty()) return false;              int val=q.top();  q.pop();              if(x[i]!=val) return false;          }      }      return true;  }  int main(){      while(scanf("%d",&n)!=EOF){          bool st=false,qu=false,pr=false;          for(int i=0;i<n;i++){              scanf("%d %d",&id[i],&x[i]);          }          st=isStack(); qu=isQueue();  pr=isPriority();          if(!st&&!qu&&!pr)  puts("impossible");          else if((!st&&qu&&pr)||(!qu&&st&&pr)||(!pr&&qu&&st)||pr&&qu&&st){              puts("not sure");          }          else if(st) puts("stack");          else if(qu) puts("queue");          else if(pr) puts("priority queue");      }      return 0;  }