#include#include#include#include#include#include#include#include#include#include#include#include#include#include#include#include#include//#include//#pragma GCC optimize(2)using namespace std;#define maxn 100005#define inf 0x7fffffff//#define INF 1e18#define rdint(x) scanf("%d",&x)#define rdllt(x) scanf("%lld",&x)#define rdult(x) scanf("%lu",&x)#define rdlf(x) scanf("%lf",&x)#define rdstr(x) scanf("%s",x)#define mclr(x,a) memset((x),a,sizeof(x))typedef long long ll;typedef unsigned long long ull;typedef unsigned int U;#define ms(x) memset((x),0,sizeof(x))const long long int mod = 1e9;#define Mod 1000000000#define sq(x) (x)*(x)#define eps 1e-5typedef pair pii;#define pi acos(-1.0)//const int N = 1005;#define REP(i,n) for(int i=0;i<(n);i++)typedef pair pii;inline int rd() { int x = 0; char c = getchar(); bool f = false; while (!isdigit(c)) { if (c == '-') f = true; c = getchar(); } while (isdigit(c)) { x = (x << 1) + (x << 3) + (c ^ 48); c = getchar(); } return f ? -x : x;}ll gcd(ll a, ll b) { return b == 0 ? a : gcd(b, a%b);}int sqr(int x) { return x * x; }/*ll ans;ll exgcd(ll a, ll b, ll &x, ll &y) { if (!b) { x = 1; y = 0; return a; } ans = exgcd(b, a%b, x, y); ll t = x; x = y; y = t - a / b * y; return ans;}*/int n;int main(){// ios::sync_with_stdio(0); while (cin >> n) { stacksk; queuequ; priority_queueq; bool fg1 = 1, fg2 = 1, fg3 = 1; for (int i = 1; i <= n; i++) { int opt; opt = rd(); if (opt == 1) { int x = rd(); if (fg1)sk.push(x); if (fg2)qu.push(x); if (fg3)q.push(x); } else { int x = rd(); if (!sk.empty() && sk.top() == x && fg1)sk.pop(); else fg1 = 0; if (!qu.empty() && qu.front() == x && fg2)qu.pop(); else fg2 = 0; if (!q.empty() && q.top() == x && fg3)q.pop(); else fg3 = 0; } } int ans = fg1 + fg2 + fg3; if (!ans)cout << "impossible" << endl; else { if (ans == 1) { if (fg1 == 1)cout << "stack" << endl; else if (fg2)cout << "queue" << endl; else if (fg3)cout << "priority queue" << endl; } else cout << "not sure" << endl; } } return 0;} EPFL - Fighting
