new_contents: # -*- coding:utf-8 -*-
  # Definition for a  binary tree node
  # class TreeNode:
  #     def __init__(self, x):
  #         self.val = x
  #         self.left = None
  #         self.right = None
  
  
  class Solution:
      # @param num, a list of integers
      # @return a tree node
      def sortedArrayToBST(self, num):
          if not num:
              return None
          lo = 0
          hi = len(num) - 1
          mid = (lo + hi) // 2
          root = TreeNode(num[mid])
          root.left = self.sortedArrayToBST(num[lo:mid])
          root.right = self.sortedArrayToBST(num[mid+1:hi+1])
          return root
  
subject: add leetcode Convert Sorted Array to Binary Search Tree