367. Valid Perfect Square

Easy

Given a positive integer num, write a function which returns True if num is a perfect square else False.

Follow up: Do not use any built-in library function such as sqrt.

# The sum of the first odd numbers is always a perfect square.
class Solution:
    def isPerfectSquare(self, num: int) -> bool:
        acc = 1

        while num > 0:
            num -= acc
            acc += 2

        return num == 0