LeetCode 367. Valid Perfect Square

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题目

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:

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Input: 16
Output: true

Example 2:

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Input: 14
Output: false

思路

Easy题打卡。二分查找，理论上最快的方法貌似是牛顿迭代。

代码

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class Solution(object):
    def isPerfectSquare(self, num):
        """
        :type num: int
        :rtype: bool
        """
        left, right = 0, 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