Description:
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
//NKW 甲级练习题1027
#pragma warning(disable:4996)
#include <stdio.h>
#include <stdlib.h>
#include <math.h>
int de[18], len = 0;
bool isprime(int n){
if (n <= 1) return false;
int sqr = (int)sqrt(1.0*n);
for (int i = 2; i <= sqr; i++) //这里第一次写的是i<sqr导致结果错误
if (n%i == 0)
return false;
return true;
}
int reverse(int n, int d){
len = 0;
do{
de[len++] = n%d;
n /= d;
} while (n != 0);
int a = 0;
for (int i = 0; i < len; i++)
a = a*d + de[i];
return a;
}
int main(){
int n, d;
while(1){
scanf("%d", &n);
if (n < 0) break;
scanf("%d", &d);
if (isprime(n) && isprime(reverse(n, d)))
printf("Yes\n");
else
printf("No\n");
}
system("pause");
return 0;
}