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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.

Example 1:

Input: num = 16
Output: true

Example 2:

Input: num = 14
Output: false

Constraints:

• 1 <= num <= 2^31 - 1

[Math] [Binary Search]

1. Sqrt(x) (Easy)
2. Sum of Square Numbers (Medium)