Week 1/13/19 of cassido's newsletter interview question of the week.

oneFive.java

import java.util.*;

/**
 * Returns all numbers < n whose digits are 1 or 5.
 * Created by Kyle Long on 1/14/19.
 */
public class oneFive {
    public static void main(String [] args){
        Scanner scan = new Scanner(System.in);
        int n = scan.nextInt();
        System.out.println(oneOrFive(n));
    }

    /**
     * Returns string of all numbers < n that contain only 1s or 5s
     * @param n The number to iterate
     * @return String of all digits < n that contain only 1s or 5s
     */
    public static String oneOrFive(int n){
        ArrayList<Integer> list = new ArrayList<>();
        for(int i = 1; i < n; i++){
            if(hasOnlyOneOrFive(i)){
                list.add(i);
            }
        }
        return Arrays.deepToString(list.toArray());
    }

    /**
     * Checks if a number only has 1s or 5s
     * @param n The number to check
     * @return Whether or not n contains only 1s or 5s
     */
    public static boolean hasOnlyOneOrFive(int n){
        int lastDigit = 0;
        while(n != 0){
            lastDigit = n % 10;
            if(lastDigit != 1 && lastDigit != 5){
                return false;
            }
            n /= 10;
        }
        return true;
    }
}