Leetcode - Happy Number Solution

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 <= 231 - 1

Solution in python

class Solution:
    def isHappy(self, n: int) -> bool:
        def digitSum(n):
            return sum(map(lambda x:x*x, map(int,list(str(n)))))
        seen = set()
        while not n in seen:
            seen.add(n)
            n = digitSum(n)
            if n == 1:
                return True
        return False