Given a positive integer num, write a function which returns True if num is a perfect square else False.

Note: Do not use any built-in library function such as sqrt.

Example 1:

Input: 16

Output: true

Example 2:

Input: 14

Output: false

class Solution:    def isPerfectSquare(self, num):        """        :type num: int        :rtype: bool        """        n = 1        while n*n<=num:            if n*n == num:                return True            n += 1        return False