202.py

"""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."""
class Solution:
    def isHappy(self, n: int) -> bool:

        def getNext(num):
            sum = 0
            while num > 0:
                digit = num % 10
                num = num // 10
                sum += digit ** 2

            return sum

        slow = n
        fast = getNext(n)

        while fast != 1 and slow != fast:
            slow = getNext(slow)
            fast = getNext(getNext(fast))

        return fast == 1