Write an algorithm to determine if a number n is "happy". A happy number is a number defined by the following process: Starting with any positive integer, replace the number by the sum of the squares of its digits, and repeat the process until the number equals 1 (where it will stay), or it loops endlessly in a cycle which does not include 1. Th…

HappyNumber.java

import java.util.ArrayList;
import java.util.HashSet;
import java.util.List;
import java.util.Set;

public class HappyNumber {

	public static void main(String[] args) {
		HappyNumber problem = new HappyNumber();
		boolean result1 = problem.isHappy(19);
		System.out.println("Expected: true, Result: " + result1);
	}
	
	/**
	 * Determine if a number n is "happy". <br/>
	 * 
	 * A happy number is a number defined by the following process: Starting with
	 * any positive integer, replace the number by the sum of the squares of its
	 * digits, and repeat the process until the number equals 1 (where it will
	 * stay), or it loops endlessly in a cycle which does not include 1. Those
	 * numbers for which this process ends in 1 are happy numbers.
	 * 
	 * @param n
	 * @return True if n is a happy number, and False if not.
	 */
    public boolean isHappy(int n) {
        
        Set<Integer> allResultSet = new HashSet<>();
        
        int result = n;
        while(result != 1) {
            result = digitsSumOfSquares(result);
            if(allResultSet.contains(result)){
                return false;
            }
            allResultSet.add(result);
        }
        
        return true;
 
    }
    
    private int digitsSumOfSquares(int number) {
        int sum = 0;
        List<Integer> digitList = findDigits(number);
        for(Integer digit : digitList) {
            sum += Math.pow( digit, 2 );
        }
        return sum;
    }
    
    private List<Integer> findDigits(int number){
        List<Integer> digits = new ArrayList<>();
        while (number > 0) {
            digits.add(0, Integer.valueOf( number % 10 ) ) ;
            number = number / 10;
        }
        return digits;
    }

}