There is a bag-like data structure, supporting two operations: 1 x Throw an element x into the bag. 2 Take out an element from the bag. Given a sequence of operations with return values, you’re going to guess the data structure. It is a stack (Last-In, First-Out), a queue (First-In, First-Out), a priority-queue (Always take out larger elements first) or something else that you can hardly imagine! Input There are several test cases. Each test case begins with a line containing a single integer n (1 ≤ n ≤ 1000). Each of the next n lines is either a type-1 command, or an integer 2 followed by an integer x. That means after executing a type-2 command, we get an element x without error. The value of x is always a positive integer not larger than 100. The input is terminated by end-of-file (EOF). Output For each test case, output one of the following: stack It’s definitely a stack. queue It’s definitely a queue. priority queue It’s definitely a priority queue. impossible It can’t be a stack, a queue or a priority queue. not sure It can be more than one of the three data structures mentioned above.
Sample Input
6 1 1 1 2 1 3 2 1 2 2 2 3 6 1 1 1 2 1 3 2 3 2 2 2 1 2 1 1 2 2 4 1 2 1 1 2 1 2 2 7 1 2 1 5 1 1 1 3 2 5 1 4 2 4
Sample Output
queue not sure impossible stack priority queue
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1 /* 2 Problem: 3 OJ: 4 User: S.B.S. 5 Time: 6 Memory: 7 Length: 8 */ 9 #include<bits/stdc++.h> 10 #include<iostream> 11 #include<cstdio> 12 #include<cstring> 13 #include<cmath> 14 #include<algorithm> 15 #include<queue> 16 #include<cstdlib> 17 #include<iomanip> 18 #include<cassert> 19 #include<climits> 20 #include<functional> 21 #include<stack> 22 #include<bitset> 23 #include<vector> 24 #include<list> 25 #define F(i,j,k) for(int i=j;i<k;++i) 26 #define M(a,b) memset(a,b,sizeof(a)) 27 #define FF(i,j,k) for(int i=j;i>=k;i--) 28 #define maxn 10001 29 #define inf 0x3f3f3f3f 30 #define maxm 4001 31 #define mod 998244353 32 #define LOCAL 33 using namespace std; 34 int read(){ 35 int x=0,f=1;char ch=getchar(); 36 while(ch<'0'||ch>'9'){if(ch=='-')f=-1;ch=getchar();} 37 while(ch>='0'&&ch<='9'){x=x*10+ch-'0';ch=getchar();} 38 return x*f; 39 } 40 int n,m; 41 struct POINT 42 { 43 int id; 44 int data; 45 friend bool operator < (POINT a,POINT b){return a.data < b.data;} 46 }d[maxn]; 47 inline bool pdstk() 48 { 49 stack<int> stk; 50 F(i,0,n){ 51 if(d[i].id==1) stk.push(d[i].data); 52 if(d[i].id==2){ 53 if(stk.empty()) return false; 54 if(stk.top()==d[i].data){stk.pop();continue;} 55 else return false; 56 } 57 } 58 return true; 59 } 60 inline bool pdque() 61 { 62 queue<int> q; 63 F(i,0,n){ 64 if(d[i].id==1) q.push(d[i].data); 65 if(d[i].id==2){ 66 if(q.empty()) return false; 67 if (q.front()==d[i].data){q.pop();continue;} 68 else return 0; 69 } 70 } 71 return true; 72 } 73 inline bool pdheap() 74 { 75 priority_queue<POINT> h; 76 F(i,0,n){ 77 if (d[i].id==1) h.push(d[i]); 78 if(d[i].id==2){ 79 if(h.empty()) return false; 80 if(h.top().data==d[i].data){h.pop();continue;} 81 else return 0; 82 } 83 } 84 return true; 85 } 86 int main() 87 { 88 std::ios::sync_with_stdio(false);//cout<<setiosflags(ios::fixed)<<setprecision(1)<<y; 89 #ifdef LOCAL 90 freopen("qu.in","r",stdin); 91 freopen("qu.out","w",stdout); 92 #endif 93 cin>>n; 94 F(i,0,n) cin>>d[i].id>>d[i].data; 95 if(pdstk()) cout<<"YES"<<endl;else cout<<"No"<<endl; 96 if(pdque()) cout<<"YES"<<endl;else cout<<"No"<<endl; 97 if(pdheap()) cout<<"YES"<<endl;else cout<<"No"<<endl; 98 return 0; 99 }