Valid Perfect Square
You are 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: trueExplanation: We return true because 4 * 4 = 16 and 4 is an integer.
Example 2:
Input: n = 15
Output: falseExplanation: We return false because square root of 15 is not an integer.
Constraints:1 <= n <= ((2^31) - 1)