Happy Number

Write a function to determine if a given positive integer is a "Happy Number."

A happy number is defined as a number that, when repeatedly replaced by the sum of the square of its digits, eventually reaches 1. If it becomes an endless loop that never reaches 1, it is not a happy number.

Your task is to implement the isHappy function, which takes an integer as input and returns a boolean indicating whether it is a happy number or not.