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

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

##1015. Reversible Primes (20)
时间限制
400 ms
内存限制
65536 kB
代码长度限制
16000 B
判题程序
Standard
作者
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

考查进制转换和数字反转。

注意函数

int number_reverse(int num, int basic)

实现了反转和转化。

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;
}

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