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`