367. Valid Perfect Square

Given a positive integer num, return true if num is a perfect square or false otherwise. A perfect square is an integer that is the square of an integer. In other words, it is the product of some integer with itself. You must not use any built-in library function, such as sqrt. Example 1: Input: num = 16 Output: true Explanation: We return true because 4 * 4 = 16 and 4 is an integer. Exampl