1015. Reversible Primes (20)

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.

73 1023 223 10-2

YesYesNo

做麻烦了，从输入的a中取出最后一位可以直接拿过来当反转的第一位来用，以此类推，没有必要再生成字符串。

import java.util.*;public class Main {	public static boolean IsPrime(int a) {		if(a==1)			return false;		else if(a==2)			return true;		else {			for(int i=2;i*i<=a;i++) {				if(a%i==0)					return false;			}			return true;		}	}	public static void main(String[] args) {		// TODO Auto-generated method stub		Scanner in=new Scanner(System.in);		int a=in.nextInt();		while(a>0) {			int radix=in.nextInt();			String as=new String("");			String ass=new String("");			int num=0;			int aa=a;			while(a>0) {				char ch;				int dig=a%radix;				ch=(char)('0'+dig);				as=ch+as;				a/=radix;			}			int len=as.length();			for(int i=len-1;i>-1;i--) {				char ch=as.charAt(i);				ass=ass+ch;			}			for(int i=0;i