PAT 甲级 1015 Reversible Primes (20 分) （进制转换和素数判断(错因为忘了=)）

1015 Reversible Primes (20 分)

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 (<) and D (1), 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:

Sample Output:

Yes

Yes

No

题目大意：

一开始理解错了题意。。。。
数字N在D进制下是不是双重素数。双重素数是本身和倒数皆为素数的数。

实现：判断N是否为素数。如果不是，输出No，否则将该数在D进制下倒过来再化为十进制数，判断是否为素数。如果是，输出Yes，否则输出No.

复习判断素数知识点注意 ‘ = ’ ！！！

#include<bits/stdc++.h>

using namespace std;

bool prime(int x){

    if(x==||x==){

        return false;

    }

    if(x==){

        return true;

    }

    for(int i=;i<=sqrt(x);i++){//这个地方忘记了=号！！！

        if(x%i==){

            return false;

        }

    }

    return true;

}

int main()

{

    int a;

    int d;

    while(cin>>a)

    {

        if(a<){

            break;

        }

        cin>>d;

        //先判断本身是不是素数

        if(!prime(a)){

            cout<<"No"<<endl;

            continue;

        }

        //根据相应地进制转

        string s="";

        int x;

        while(a){

            s+=char(a%d+'');

            a=a/d;

        }

        //cout<<s<<endl;    

        //反向再把它从d进制转成10进制

        int l = s.length();

        x=;

        for(int i=;i<l;i++){

            x=x*d+s[i]-'';

        }

        //cout<<x<<endl;

        if(prime(x)){

            cout<<"Yes"<<endl;

        }

        else{

            cout<<"No"<<endl;

        }

    }

    return ;

 }

巴特西

PAT 甲级 1015 Reversible Primes (20 分) （进制转换和素数判断(错因为忘了=)）

Input Specification:

Output Specification:

Sample Input:

Sample Output:

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