Given a positive integer num, write a function which returns True if num is a perfect square else False. Follow up: Do not use any built-in library function such as sqrt.
Example 1: Input: num = 16 Output: true
- code
class Solution:
def isPerfectSquare(self, num: int) -> bool:
l, r = 1, num
while l <= r:
mid = l + (r-l) // 2
if mid * mid < num:
l = mid + 1
elif mid * mid > num:
r = mid - 1
else:
return True
return False