11995 - I Can Guess the Data Structure!

uva-11995.cpp

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

using namespace std;

int main(void) {
  int n;
  while(scanf("%d", &n) != EOF) {
    int cmd, num;
    bool isStack = true, isQueue = true, isPQueue = true;
    stack<int> s;
    queue<int> q;
    priority_queue<int> pq;
    while(n--) {
      scanf("%d %d", &cmd, &num);
      switch(cmd) {
        case 1:
          s.push(num);
          q.push(num);
          pq.push(num);
          break;
        default:
          if(s.empty() || s.top() != num) isStack = false;
          if(q.empty() || q.front() != num) isQueue = false;
          if(pq.empty() || pq.top() != num) isPQueue = false;
          if(!s.empty()) s.pop();
          if(!q.empty()) q.pop();
          if(!pq.empty()) pq.pop();
          break;
      }
    }
    if(isStack + isQueue + isPQueue > 1)
      printf("not sure\n");
    else if(isStack) printf("stack\n");
    else if(isQueue) printf("queue\n");
    else if(isPQueue) printf("priority queue\n");
    else printf("impossible\n");
  }
  return 0;
}