Valid Perfect Square

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 assqrt.

Example 1:

Input: 16
Returns: True

Example 2:

Input: 14
Returns: False

Binary Search

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

其他解法：http://www.cnblogs.com/grandyang/p/5619296.html

二刷：

class Solution(object):
    def isPerfectSquare(self, num):
        """
        :type num: int
        :rtype: bool
        """
        start, end = 1, num
        while start +1 < end:
            mid = (start+end)/2
            if mid*mid < num:
                start = mid
            else:
                end = mid
        if start*start == num or end*end == num:
            return True
        return False