// CSE 142, Autumn 2007, Marty Stepp
//
// This program demonstrates fencepost loops and boolean logic
// in methods about counting and printing factors of an integer.

import java.util.*;   // for Scanner

public class Factors3 {
    public static void main(String[] args) {
        printFactors(24);
        printFactors2(24);

        Scanner console = new Scanner(System.in);
        System.out.print("Type a number: ");
        int number = console.nextInt();
        if (isPrime(number)) {
            System.out.println(number " is a prime number.");
        } else {
            System.out.println(number " isn't prime.");
        }
    }
    
    // Prints the factors of the given number.
    // For example, printFactors(24) prints [1, 2, 3, 4, 6, 8, 12, 24].
    // This is an example of a fencepost problem.
    public static void printFactors(int n) {
        System.out.print("[" + 1);
        for (int i = 2; i <= n; i++) {
            if (n % i == 0) {
                // i is a factor of n
                System.out.print(", " + i);
            }
        }
        System.out.println("]");
    }
    
    // Prints the factors of the given number, other than 1 and n itself.
    // For example, printFactors(24) prints [2, 3, 4, 6, 8, 12].
    // This is another example of a fencepost problem.
    public static void printFactors2(int n) {
        System.out.print("[");
        int count = 0;
        for (int i = 2; i <= n - 1; i++) {
            if (n % i == 0) {
                // i is a factor of n
                count++;
                if (count > 1) {
                    System.out.print(", " + i);
                } else {
                    System.out.print(i);
                }
            }
        }
        System.out.println("]");
    }
    
    // Returns true if the given number is prime, or false if not.
    public static boolean isPrime(int n) {
        if (countFactors(n) == 2) {
            return true;
        } else {
            return false;
        }
    }
    
    // Returns how many factors the given number has.
    // Assumes n is non-negative.
    public static int countFactors(int n) {
        int count = 0;
        for (int i = 1; i <= n; i++) {
            if (n % i == 0) {
                // i is a factor of n
                count++;
            }
        }
        return count;
    }
}