69. Sqrt(x)

题目 https://leetcode.com/problems/sqrtx/description/

好笨的方法：

class Solution:
    def mySqrt(self, x):
        """
        :type x: int
        :rtype: int
        """
        if 0 < x and  ( x == 1 or x == 0):
            return x
        if x == 2 or x == 3:
            return 1
        if x <= 7 and x >=4:
            return 2
        right = x //2
        left = right//2
        while (right - left >1):
                if right**2 > x and left**2 > x :
                    left = left // 2
                    right = right // 2
                elif left**2 < x and right**2 > x:
                    if ((right + left) // 2)**2 < x:
                        left = (right + left) // 2
                    else:
                        right = (right + left) // 2
                elif left**2 == x:
                    return left
                elif right**2 ==x :
                    return right
                # print('left,right',left,right)
        if right**2 == x:
            return right
        return left

引入一个mid，就变得好看多了：

class Solution:
    def mySqrt(self, x):
        """
        :type x: int
        :rtype: int
        """

        if x == 0:
            return 0
        left, right = 1, x
        mid = 0
        while (right - left) > 1:
            mid = (left + right) // 2
            if mid * mid > x:
                right = mid
            else:
                left = mid
        return left