Leetcode 367. Valid Perfect Square

Problem

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.

Algorithm

Use bineary search to get the sqrt root first and then test with accuracy.

Code

class Solution:
    def isPerfectSquare(self, num: int) -> bool:
        L, R = 0, num
        while R - L > 1e-3:
            Mid = (L + R) * 0.5
            if Mid * Mid > num:
                R = Mid
            else: 
                L = Mid
        R = int(R)
        if fabs(num - R*R) < 1e-9:
            return True
        else:
            return False