UVA 11995 - I Can Guess the Data Structure! (数据结构） STL的应用

原题：

 

 

Problem I

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). The size of input file does not exceed 1MB.

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

Output for the Sample Input

queue
not sure
impossible
stack
priority queue

 

 

 

 

/**
*  刚开始学用STL。 很方便。  不过还是再犹豫，该不该常用。。
*/

#include <cstdio>
#include <cstring>
#include <cmath>
#include <stack>
#include <string>
#include <queue>
#include <algorithm>
#define INF 0x7fffffff

using namespace std;

stack<int> filo;
queue<int> fifo;
priority_queue<int> pri;
int main()
{
    int n, i;
    while(scanf("%d", &n) != EOF ) {
        while(filo.empty() == false) filo.pop();
        while(fifo.empty() == false) fifo.pop();
        while(pri.empty() == false) pri.pop();
        int type, num, isStack = 1, isQueue = 1, isPriority = 1;
        i = 0;
        while(n --) {
            int curNum;
            scanf("%d%d", &type, &num);

            if(type == 1){
                fifo.push(num);
                filo.push(num);
                pri.push(num);
            } else {
                if(isStack) {
                    if(filo.empty()) {isStack = 0; }
                    else {
                        curNum = filo.top();
                        filo.pop();
                        if(curNum != num) {isStack = 0; }
                    }
                }
                if(isQueue) {
                    if(fifo.empty()) { isQueue = 0; }
                    else {
                        curNum = fifo.front();
                        fifo.pop();
                        if(curNum != num) {isQueue = 0; }
                    }
                }
                if(isPriority) {
                    if(pri.empty()) { isPriority = 0; }
                    else {
                        curNum = pri.top();
                        pri.pop();
                        if(curNum != num) { isPriority = 0; }
                    }
                }
            }
        }

        if(isStack && !isQueue && !isPriority) printf("stack\n");
        else if(isQueue && !isStack && !isPriority) printf("queue\n");
        else if(isPriority && !isStack && !isQueue) printf("priority queue\n");
        else if(!isStack && !isQueue && !isPriority) printf("impossible\n");
        else printf("not sure\n");
    }
    return 0;
}