1015 Reversible Primes (20)

题目信息

A reversible prime in any number system is a prime whose "reverse" in that number system is also a prime. For example in the decimal system 73 is a reversible prime because its reverse 37 is also a prime.
Now given any two positive integers N (< 10⁵) and D (1 < D <= 10), you are supposed to tell if N is a reversible prime with radix D.
Input Specification:
The input file consists of several test cases. Each case occupies a line which contains two integers N and D. The input is finished by a negative N.
Output Specification:
For each test case, print in one line "Yes" if N is a reversible prime with radix D, or "No" if not.
Sample Input:
73 10
23 2
23 10
-2
Sample Output:
Yes
Yes
No

心得

又是刷PAT的一天，1014题还有一个测试点没通过。
只有一个感慨：论头发是怎么没的......

代码

#include<cstdio>
#include<cmath>
#include<vector>
bool isPrime(int n){
    if(n<=1) return false;
    int sqr=(int)sqrt(n*1.0);
    for(int i=2;i<=sqr;i++){
        if(n%i==0) return false;
    }
    return true;
}
using namespace std;
int main(){
    int n=1,d;//n<100000&&d<=10
    scanf("%d",&n);
    while(n>=0){
        scanf("%d",&d);
        int before=n;
        int ver=0;
        vector<int> v;
        while(n>0){
            v.push_back(n%d);
            n/=d;
        }   
        for(int i=0;i<v.size();i++){
            ver*=d;ver+=v[i];
        }
        if(isPrime(before)&&isPrime(ver)) printf("Yes\n");
        else printf("No\n");
        scanf("%d",&n);
    }
    return 0;
}

测试结果