[UVa] 11995 I Can Guess the Data Structure.cpp

#include <cstdio>
#include <stack>
#include <queue>
using namespace std;
int main()
{
 //   freopen("input.txt","rt",stdin);
    int N, Command, num;
    while (scanf("%d", &N) != EOF) {
        stack<int> S;
        queue<int> Q;
        priority_queue<int> PQ;
        bool isStack = 1, isQueue = 1, isPriQueue = 1;

        while (N--) {
            scanf("%d%d", &Command, &num);
            if (Command == 1) {
                S.push(num);
                Q.push(num);
                PQ.push(num);
            }
            else {
                if (S.empty() || S.top() != num) isStack = 0;
                if (Q.empty() || Q.front() != num) isQueue = 0;
                if (PQ.empty() || PQ.top() != num) isPriQueue = 0;
                if (!S.empty()) S.pop();
                if (!Q.empty()) Q.pop();
                if (!PQ.empty()) PQ.pop();
            }
        }
        if (isStack + isQueue + isPriQueue > 1)
            puts("not sure");
        else if (isStack) puts("stack");
        else if (isQueue) puts("queue");
        else if (isPriQueue) puts("priority queue");
        else puts("impossible");
    }
    return 0;
}