202 Happy Number (David)

Here we solve the Happy Number Problem from LeetCode.

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, 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.

Return True if n is a happy number, and False if not.

Example:

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

The trick to this problem is you have to keep a record of the happy numbers already encountered, and you have to be able to iterate through the individual digits of a number. In this approach, I used a set previous_numbers to keep track of the happy numbers that have already been calculated. I also converted the numbers to strings, since strings are iterable by character in Python (each character being a digit in this case) , instead of using // and %.

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

        current_number = str(n)
        previous_numbers = set()

        while current_number != '1':

            square_sum = 0

            for digit in map(int,list(str(current_number))):
                square_sum += digit * digit

            current_number = str(square_sum)

            if current_number not in previous_numbers:
                previous_numbers.add(current_number)
            else:
                return False

        return True

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