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.
Input: num = 16
Output: true
Explanation: We return true because 4 * 4 = 16 and 4 is an integer.
Input: num = 14
Output: false
Explanation: We return false because 3.742 * 3.742 = 14 and 3.742 is not an integer.
- 1 <= num <= 231 - 1