367. 有效的完全平方数

class Solution:
   def isPerfectSquare(self, num: int) -> bool:
       if num == 0 or num == 1:
           return True

       l, r = 1, num
       while l <= r:
           mid = (l + r) // 2
           if mid * mid == num:
               return True
           elif mid * mid < num:
               l = mid + 1
           else:
               r = mid - 1
       return False