Write a Java function named isPerfectSquare that takes a positive integer n and returns true if it is a perfect square, and false otherwise.
You must not use Math.sqrt() or any other library method for square roots.

Instead, use the fact that the sum of the first k odd numbers equals k².
Use a loop to subtract consecutive odd numbers (1, 3, 5, 7, …) from n until you either reach 0 (which means it's a perfect square) or go negative (which means it's not).