UVA 1995 I can guess the structer

模 拟

 /*by SilverN*/
 #include<algorithm>
 #include<iostream>
 #include<cstring>
 #include<cstdio>
 #include<cmath>
 #include<vector>
 #include<queue>
 #include<stack>
 using namespace std;
 int read(){
     int x=,f=;char ch=getchar();
     while(ch<'' || ch>''){if(ch=='-')f=-;ch=getchar();}
     while(ch>='' && ch<=''){x=x*+ch-'';ch=getchar();}
     return x*f;
 }
 priority_queue<int>q;
 stack<int>st;
 queue<int>que;
 int n;
 int x,y;
 bool flag_st,flag_qu,flag_pr;
 int main(){
 /*    freopen("qu.in","r",stdin);
     freopen("qu.out","w",stdout);*/

     while(scanf("%d",&n)!=EOF){
         int i,j;
         flag_pr=flag_qu=flag_st=;
         while(!q.empty()) q.pop();
         while(!st.empty()) st.pop();
         while(!que.empty()) que.pop();
         for(i=;i<=n;i++){
             scanf("%d%d",&x,&y);
             if(x==){
                 q.push(y);
                 st.push(y);
                 que.push(y);
             }
             else{
                 if(q.empty() || q.top()!=y)flag_pr=;
                 if(st.empty() || st.top()!=y)flag_st=;
                 if(que.empty() || que.front()!=y)flag_qu=;
                 if(!q.empty())q.pop();
                 if(!st.empty()) st.pop();
                 if(!que.empty()) que.pop();
             }
         }
         int cnt=;
         if(flag_st)cnt++; if(flag_pr)cnt++; if(flag_qu)cnt++;
         if(cnt>){
             printf("not sure\n");
             continue;
         }
         if(flag_st && !flag_pr && !flag_qu)printf("stack\n");
         if(!flag_st && !flag_pr && flag_qu)printf("queue\n");
         if(!flag_st && flag_pr && !flag_qu)printf("priority queue\n");
         if(!flag_st && !flag_pr && !flag_qu)printf("impossible\n");
     }
     return ;
 }