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
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 stubScanner 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<len;i++) {char ch=ass.charAt(i);num=num*radix+(int)(ch-'0');}if(IsPrime(num)&&IsPrime(aa))System.out.println("Yes");elseSystem.out.println("No");a=in.nextInt();}}}