From LeetCode 202. 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.


class Solution:
    def isHappy(self, n: int) -> bool:
        def calculate_happy(num):
            sum_ = 0
            # sum of square of each digit
            while num:
                sum_ += (num % 10) ** 2
                num = num // 10
            return sum_

        # record
        record = set()

        while True:
            n = calculate_happy(n)
            if n == 1:
                return True
            # if an element repeats in set, means we are in a loop
            if n in record:
                return False