Description
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.
Example 1:
Input: num = 16 Output: true Explanation: We return true because 4 * 4 = 16 and 4 is an integer.
Example 2:
Input: num = 14 Output: false Explanation: We return false because 3.742 * 3.742 = 14 and 3.742 is not an integer.
Constraints:
1 <= num <= 231 - 1
Solution
Python3
class Solution:
def isPerfectSquare(self, num: int) -> bool:
left, right = 1, 10 ** 18
while left < right:
mid = left + (right - left) // 2
if mid * mid >= num:
right = mid
else:
left = mid + 1
return left * left == num