点击链接PAT甲级-AC全解汇总

题目：
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 (<10^​5​​ ) and D (1

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
1
2
3
4

Sample Output:

Yes
Yes
No
1
2
3

题意：
一行输入两个数字ab，判断a本身是不是素数，a经过b进制转换后逆序再转换回来后，是不是素数，如果都是素数则输出yes，否则no

我的代码：

#include
using namespace std;

bool is_prime(int num)
{
    if(num==0||num==1)return false;
    for(int i=2;i<=sqrt(num);i++)
        if(num%i==0)return false;
    return true;
}
int main()
{
    int num,radix;
    cin>>num;
    while(num>=0)
    {
        cin>>radix;
        if(!is_prime(num))cout<<"No"<<endl;
        else
        {
            //转成radix进制,同时逆序
            string str;
            while(num)
            {
                str+=num%radix+'0';
                num/=radix;
            }
            //转成int
            int ans=0;
            for(int i=0;i<str.length();i++)
            {
                ans=ans*radix+(str[i]-'0');
            }
            //判断素数
            if(is_prime(ans))cout<<"Yes"<<endl;
            else cout<<"No"<<endl;
        }
        cin>>num;
    }
    return 0;
}

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