uva-11995

11995 - I Can Guess the Data Structure!

　　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

题意：水。。。

代码：

#include<iostream>
#include<cstdio>
#include<cstring>
#include<cmath>
#include<algorithm>
#include<queue>
#include<vector>
#include<stack>
using namespace std;
const int INF=0x3f3f3f3f;
#define mem(x,y) memset(x,y,sizeof(x))
#define SI(x) scanf("%d",&x)
#define SL(x) scanf("%lld",&x)
#define PI(x) printf("%d",x)
#define PL(x) printf("%lld",x)
#define P_ printf(" ")
#define T_T while(T--)
#define F(i,s,x) for(i=s;i<x;i++)
const double PI=acos(-1.0);
typedef long long LL;
int main(){
	int n;
	while(~SI(n)){
		int x,t;
		queue<int>q;
		priority_queue<int>sq;
		stack<int>S;
		int a=1,b=1,c=1;
		int temp=0;
		while(n--){
			SI(t);SI(x);
			if(temp)continue;
			if(t==1){
				q.push(x);
				sq.push(x);
				S.push(x);
			}
			else{
				if(q.empty())temp=1;
				if(temp)continue;
				if(q.front()!=x)a=0;
				if(sq.top()!=x)b=0;
				if(S.top()!=x)c=0;
				q.pop();
				sq.pop();
				S.pop();
			}
		}
		if(temp||(a+b+c==0))puts("impossible");
		else if(a+b+c>1)puts("not sure");
		else if(a)puts("queue");
		else if(b)puts("priority queue");
		else if(c)puts("stack");
	}
	return 0;
}