0202. Happy Number

"""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:
12 + 92 = 82
82 + 22 = 68
62 + 82 = 100
12 + 02 + 02 = 1

Example 2:
Input: n = 2
Output: false
 
Constraints:
1 <= n <= 2^31 - 1"""


class Solution:
    def isHappy(self, n: int) -> bool:
        s = set() # make a stop sign for while loop
        while n not in s: 
            s.add(n)
            n = sum([int(x) **2 for x in str(n)])
        return n == 1