Perfect Square

Problem

Given a positive integer num, check whether it is a perfect square. 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.

Examples

isPerfectSquare(25)
// returns true
// 25 forms a perfect square because 5 * 5 = 25.

isPerfectSquare(36)
// returns true
// 36 forms a perfect square because 6 * 6 = 36.

isPerfectSquare(15)
// returns false
// No integer multiplied by itself gives a wave height of 15.