Happy Number (LeetCode #202)

Challenge Statement

• 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.
• This challenge corresponds to LeetCode #202.

Constraints

• 1 <= n <= 231 - 1

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

Solution

Below is my solution and some test cases. This solution has a logarithmic time complexity O(log n) and a constant space complexity O(1), where n is the length of the input list.