Silvestri's Solution to Emirp Homework

EmirpGenerator.java

/*
 * Name: Prof. Antonio C. Silvestri
 * Date: 09/16/18
 * Course Number: CSC-220
 * Course Name: Data Structures
 * Problem Number: HW1
 * Email: silvestri@stcc.edu
 * Short Description of the Problem
 */

import java.util.Scanner;

public class EmirpGenerator {
	private static boolean isPrime(int num) {
		for (int i = 2; i <= (int) (Math.sqrt(num)); i++)
			if (num % i == 0)
				return false;
		return true;
	}

	private static int reverseInt(int num) {
		int revInt = 0;
		int sign = 1;
		if (num < 0) {
			sign = -1;
			num = -num;
		}
		while (num > 0) {
			int lastDigit = num % 10;
			revInt = 10 * revInt + lastDigit;
			num /= 10;
		}
		return sign * revInt;
	}

	private static boolean isPalindromic(int num) {
		return num == reverseInt(num);
	}

	private static boolean isEmirp(int num) {
		if (!isPrime(num))
			return false;
		if (isPalindromic(num))
			return false;
		if (!isPrime(reverseInt(num)))
			return false;
		return true;				
	}
	
	private static String generateEmirps(int start, int noOfEmirps) {
		String output = "";
		int count = 0;
		int num = start;
		while (count < noOfEmirps) {
			if (isEmirp(num)) {
				output += String.format("%7d ", num);
				count++;
				if (count % 10 == 0)
					output += "\n";
			}
			num++;
		}
		return output;
	}

	// **********************************************

	private static void process(Scanner sc, String args[]) {
		System.out.print("Enter Emirp Starting Point: ");
		int start = sc.nextInt();
		System.out.print("Enter number of Emirps: ");
		int noOfEmpirps = sc.nextInt();
		sc.nextLine(); // IMPORTANT!! Reset Scanner
		String output = generateEmirps(start, noOfEmpirps);
		System.out.println(output);
	}

	// **********************************************

	private static boolean doThisAgain(Scanner sc, String prompt) {
		System.out.print(prompt);
		String doOver = sc.nextLine();
		return doOver.equalsIgnoreCase("Y");
	}

	// **********************************************

	public static void main(String args[]) {
		final String TITLE = "EMIRP Generator V1.1";
		final String CONTINUE_PROMPT = "Do this again? [y/N] ";

		System.out.println("Welcome to " + TITLE);
		Scanner sc = new Scanner(System.in);
		do {
			process(sc, args);
		} while (doThisAgain(sc, CONTINUE_PROMPT));
		sc.close();
		System.out.println("Thank you for using " + TITLE);
	}

}