1015. Reversible Primes (20)

超、凢脫俗 2022-05-31 08:35 105阅读 0赞

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

--------------------

题目大意：

任何数字系统中的可逆素数都是质数，其“逆”在这个数字系统中也是一个素数。例如，在十进制系统中，73是一个可逆质数，因为他的逆37也是一个素数。  
现在给定任意两个正整数N(<105)和（1<D<=10）,你应该判断出在D进制下N是否为一个可逆素数。  
输入规格：  
输入文件有几个测试用例组成。每个测试用例占一行包括两个整数N和D。输入一个负数N结束。  
输出规范：  
对于每个测试用例，如果N在D进制下是可逆素数dayinchu"Yes"否则打印"No"。

代码：

#include<stdio.h>
    #include<math.h>
    bool is_prime(int x)
    {
        if(x<2)
            return false;
        int i;
        for(i=2;i<=sqrt(x);i++)
        {
           if(x%i==0)
                break;
        }
        if(i<=sqrt(x))
            return false;
        else
            return true;
    }
    int exchange(int x,int radix)
    {
        int i=0,a[100],j,n=0;
        while(x)
        {
           a[i++]=x%radix;
          // printf("%d\n",x%radix);
           x/=radix;
    
        }
        for(j=0;j<i;j++)
        {
            n*=radix;
            n+=a[j];
        }
        return n;
    }
    int main()
    {
        int i,j,n,m,k,t;
        bool flag1,flag2;
        while(scanf("%d",&n)!=EOF&&n>0)
        {
            flag1=is_prime(n);
            scanf("%d",&m);
            k=exchange(n,m);
            flag2=is_prime(k);
            if(flag1&&flag2)
                printf("Yes\n");
            else
                printf("No\n");
        }
        return 0;
    }