## PAT (Advanced Level)-1015. Reversible Primes (20)

PAT (Advanced Level)-1015. Reversible Primes (20)

##1015. Reversible Primes (20)

400 ms

65536 kB

16000 B

Standard

CHEN, Yue

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``````

## 解读

``int number_reverse(int num, int basic)``

## 完整代码

``````#include<iostream>

using namespace std;

int number_reverse(int num, int basic)
{
int num_2 = 0;
for (; num;)
{
num_2 *= basic;
num_2 += num%basic;
num /= basic;
}
return num_2;
}

bool is_Prime(int num)
{
if (num < 2)
return false;
else if (num == 2 || num == 3)
return true;
else
{
for (int i = 2; i*i <= num; i++)
{
if (num%i == 0)
return false;
}
return true;
}
}

int main()
{
int N = 0;
for (;;)
{
cin >> N;
if (N < 0)
break;
int D;
cin >> D;
if (is_Prime(N) && is_Prime(number_reverse(N, D)))
{
cout << "Yes" << endl;
}
else
{
cout << "No" << endl;
}

}
return 0;
}``````