UVA 11995 I Can Guess the Data Structure!

 1 #include <iostream>
 2 #include <cstring>
 3 #include <queue>
 4 #include <stack>
 5 using namespace std;
 6 
 7 
 8 
 9 int main (){
10     int n;
11     int x[1005][2];
12     while (cin>>n){
13         for (int i=0;i<n;i++){
14             cin>>x[i][1]>>x[i][0];
15         }
16         queue<int> q1;
17         stack<int> q2;
18         priority_queue<int> q3;
19         int flag[5];
20         for (int i=0;i<5;i++)  flag[i]=1;
21         for (int i=0;i<n;i++){
22             if (x[i][1]==1){
23                 q1.push (x[i][0]);
24                 q2.push (x[i][0]);
25                 q3.push (x[i][0]);
26             }
27             else {
28                 if (flag[1]&&(q1.empty()||q1.front()!=x[i][0])){
29                     flag[1]=0;
30                 }
31                 if (flag[1])
32                     q1.pop ();
33                 if (flag[2]&&(q2.empty()||q2.top()!=x[i][0])){
34                     flag[2]=0;
35                 }
36                 if (flag[2])
37                     q2.pop ();
38                 if (flag[3]&&(q3.empty()||q3.top()!=x[i][0])){
39                     flag[3]=0;
40                 }
41                 if (flag[3])
42                     q3.pop ();
43                 
44                 
45             }
46         }
47         int temp=0;
48         for (int i=1;i<=3;i++)
49             temp+=flag[i];
50         if (temp==0)
51             cout<<"impossible"<<endl;
52         else if (temp>=2)
53             cout<<"not sure"<<endl;
54         else if (temp==1){
55             if (flag[1])
56                 cout<<"queue"<<endl;
57             else if (flag[2])
58                 cout<<"stack"<<endl;
59             else 
60                 cout<<"priority queue"<<endl;
61         }
62         
63     }
64     return 0;
65 }