PAT-A 1015. Reversible Primes

1015. Reversible Primes

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

程序代码:

#include<stdio.h>
#include<math.h>
#include<string.h>
int convert(int n,int d);
int isPrime(int n);
int main()
{
	int N,D;
	int ans;
	while(1)
	{
		scanf("%d",&N);
		if(N<0)
			break;
		scanf("%d",&D);
		ans= convert(N,D);
		if(isPrime(N)&&isPrime(ans))
		{
			printf("Yes\n");
		}
		else
			printf("No\n");
	}
}
int convert(int n,int d)
{
	char ans[100]={0};
	int  i=0;
	while(n)
	{
		ans[i++]=n%d+'0';
		//此处必须保存字符，不能直接保存数字，因为0与字符串结束符'\0'的值一样
		n=n/d;
	}
	ans[i]='\0';
	int sum = 0;
	int len = strlen(ans);
	for(i=0;i<len;i++)
	{
		sum = sum*d+(ans[i]-'0');
	}
	return sum;
}
int isPrime(int n)   
{
	if(n<2)
		return 0;
	int i=2;
	for(i=2;i<=sqrt(n);i++){
		if((n%i)==0)
			return 0;
	}
	return 1;
}