69. Sqrt(x)

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

Implement int sqrt(int x).

Compute and return the square root of x, where x is guaranteed to be a non-negative integer.

Since the return type is an integer, the decimal digits are truncated and only the integer part of the result is returned.

Example 1:

Input: 4
Output: 2

Example 2:

Input: 8
Output: 2
Explanation: The square root of 8 is 2.82842..., and since 
             the decimal part is truncated, 2 is returned.

Solution:

class Solution(object):
    def mySqrt(self, x):
        """
        :type x: int
        :rtype: int
        """
        r = x
        while r*r>x:
            r = (r+x/r)/2
        return r