108 convert sorted array to binary search tree
108. Convert Sorted Array to Binary Search Tree
题目: https://leetcode.com/problems/convert-sorted-array-to-binary-search-tree/
难度: Medium
思路：
递归
- nums为空，return None
- nums非空，nums[n/2]为中间元素，根结点，nums[:mid]为左子树， nums[mid+1:]为右子树
class Solution(object):
def sortedArrayToBST(self, nums):
"""
:type nums: List[int]
:rtype: TreeNode
"""
if not nums:
return None
if nums:
mid = len(nums) / 2
root = TreeNode(nums[mid])
root.left = self.sortedArrayToBST(nums[:mid])
root.right = self.sortedArrayToBST(nums[mid+1:])
return root
