Happy Number.py

'''
Write an algorithm to determine if a number 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. Those numbers for which this process ends in 1 are happy numbers.

Example: 

Input: 19
Output: true
Explanation: 
12 + 92 = 82
82 + 22 = 68
62 + 82 = 100
12 + 02 + 02 = 1
'''

class Solution(object):
    def isHappy(self, n):
        """
        :type n: int
        :rtype: bool
        """
        box = set([n])
        return self.happy(n, box)
    
    def happy(self, n, box):
        if n == 1:
            return True
        
        res = 0
        while n > 0:
            res += (n % 10) ** 2
            n //= 10
        
        if res != 1 and res in box:
            return False
        box.add(res)
        
        return self.happy(res, box)