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`.

**Example 1:**

**Input:** num = 16

**Output:** true

**Example 2:**

**Input:** num = 14

**Output:** false

**Constraints:**

*   `1 <= num <= 2^31 - 1`