Leetcode 69. Sqrt(x)

Implement int sqrt(int x).

思路： Binary Search　　

 class Solution(object):
     def mySqrt(self, x):
         """
         :type x: int
         :rtype: int
         """
         l = 0
         r = x

         while l <= r:
             mid = (l+r)//2
             if mid*mid < x:
                 l = mid + 1
             elif mid*mid > x:
                 r = mid - 1
             else:
                 return mid
         return r