HappyNumber.java

// Source : https://leetcode.com/problems/happy-number/
// Author : Diego Ruiz Piqueras (Pikeras72)
// Date   : 24-04-2022

/***************************************************************************************************** 
 *
 * 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.
 * 
 * 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.
 * 
 * Return true if n is a happy number, and false if not.
 * 
 * Example 1:
 * 
 * Input: n = 19
 * Output: true
 * Explanation:
1^2 + 9^2 = 82
8^2 + 2^2 = 68
6^2 + 8^2 = 100
1^2 + 0^2 + 0^2 = 1
 * 
 * Example 2:
 *
 * Input: n = 2
 * Output: false
 *
 * Constraints:
 * 
 *  1 <= n <= 2^31 - 1
 ******************************************************************************************************/

class Solution {
    public boolean isHappy(int n) {       
        while(n != 1){
            if(n == 7)
                return true;
            else if(n <= 9)
                return false;
            int num = 0;
            while(n > 0){
                num += Math.pow(n % 10, 2);
                n /= 10;
            }
            n=num;
        }
        return true;
    }
}