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
本题可以用binary search。
class Solution(object):
def isPerfectSquare(self, num):
"""
:type num: int
:rtype: bool
"""
low, high = 1, num
while low <= high:
mid = (high + low)//2
if mid**2 == num:
return True
elif mid**2 > num:
high = mid - 1
else:
low = mid + 1
return False