SimplyEmirp.java

/**
 * An integer greater than 1 is called a prime number if its only positive divisors (factors) are 1 and itself.
 * Prime numbers have been studied over the years by a lot of mathematicians. Applications of prime
 * numbers arise in Cryptography and Coding Theory among others.
 * Have you tried reversing a prime? For most primes, you get a composite (43 becomes 34). An
 * Emirp (Prime spelt backwards) is a Prime that gives you a different Prime when its digits are reversed.
 * For example, 17 is Emirp because 17 as well as 71 are Prime.
 * In this problem, you have to decide whether a number N is Non-prime or Prime or Emirp. Assume
 * that 1 < N < 1000000.
 * Interestingly, Emirps are not new to NTU students. We have been boarding 199 and 179 buses for
 * quite a long time!
 * Input
 * Input consists of several lines specifying values for N.
 * Output
 * For each N given in the input, output should contain one of the following:
 * 1. ‘N is not prime.’, if N is not a Prime number.
 * 2. ‘N is prime.’, if N is Prime and N is not Emirp.
 * 3. ‘N is emirp.’, if N is Emirp.
 * Sample Input
 * 17
 * 18
 * 19
 * 179
 * 199
 * Sample Output
 * 17 is emirp.
 * 18 is not prime.
 * 19 is prime.
 * 179 is emirp.
 * 199 is emirp.
 */

//https://uva.onlinejudge.org/index.php?option=com_onlinejudge&Itemid=8&page=show_problem&problem=1176


import java.math.BigInteger;
import java.util.Scanner;

public class SimplyEmirp {

	public static void main(String[] args) {
		Scanner input = new Scanner(System.in);
		while (input.hasNext()) {
			String inputGiven = input.next();
			BigInteger number = new BigInteger(inputGiven);
			if (!number.isProbablePrime(10)) {
				System.out.println(number + " is not prime.");
			} else {
				String numberReversedAsString = new StringBuilder(
						number.toString()).reverse().toString();
				BigInteger numberReversed = new BigInteger(
						numberReversedAsString);
				if (numberReversed.isProbablePrime(10)
						&& numberReversed.compareTo(number) != 0) {
					System.out.println(number + " is emirp.");
				} else {
					System.out.println(number + " is prime.");
				}
			}
		}
	}
}