UVA 11995

Problem II 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

61 11 21 32 12 22 361 11 21 32 32 22 121 12 241 21 12 12 271 21 51 11 32 51 42 4

Output for the Sample Input

queuenot sureimpossiblestackpriority queue

Rujia Liu's Present 3: A Data Structure Contest Celebrating the 100th Anniversary of Tsinghua University
Special Thanks: Yiming Li

Note: Please make sure to test your program with the gift I/O files before submitting!

 

直接對三種資料結構進行類比，注意當前資料結構為空白的時候的判斷。

#include<cstdio>#include<stack>#include<queue>using namespace std;const int maxn = 1000+100;int id[maxn],x[maxn],n;bool isStack(){    stack<int> s;    for(int i=0;i<n;i++){        if(id[i]==1) s.push(x[i]);        else{            if(s.empty())  return false;            int val=s.top();  s.pop();            if(x[i]!=val) return false;        }    }    return true;}bool isQueue(){     queue<int >q;      for(int i=0;i<n;i++){        if(id[i]==1) q.push(x[i]);        else{            if(q.empty()) return false;            int val=q.front();  q.pop();            if(x[i]!=val) return false;        }    }    return true;}bool isPriority(){    priority_queue<int > q;      for(int i=0;i<n;i++){        if(id[i]==1) q.push(x[i]);        else{             if(q.empty()) return false;            int val=q.top();  q.pop();            if(x[i]!=val) return false;        }    }    return true;}int main(){    while(scanf("%d",&n)!=EOF){        bool st=false,qu=false,pr=false;        for(int i=0;i<n;i++){            scanf("%d %d",&id[i],&x[i]);        }        st=isStack(); qu=isQueue();  pr=isPriority();        if(!st&&!qu&&!pr)  puts("impossible");        else if((!st&&qu&&pr)||(!qu&&st&&pr)||(!pr&&qu&&st)||pr&&qu&&st){            puts("not sure");        }        else if(st) puts("stack");        else if(qu) puts("queue");        else if(pr) puts("priority queue");    }    return 0;}