Write an algorithm to determine if a number n is happy.

A happy number is 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 that does not include 1.
• Numbers for which this process ends in 1 are happy.

Return true if n is a happy number, and false if not.

Example:

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

Constraints: 1 <= n <= 2^31 - 1