valid-perfect-square.py

# Time:  O(logn)
# Space: O(1)

# 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
# Returns: True
# Example 2:
#
# Input: 14
# Returns: False

class Solution(object):
    def isPerfectSquare(self, num):
        """
        :type num: int
        :rtype: bool
        """
        left, right = 1, num
        while left <= right:
            mid = left + (right - left) / 2
            if mid >= num / mid:
                right = mid - 1
            else:
                left = mid + 1
        return left == num / left and num % left == 0