leetcode之Convert Sorted Array to Binary Search Tree

# Definition for a binary tree node.
# class TreeNode(object):
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None

class Solution(object):
def sortedArrayToBST(self, nums):
"""
:type nums: List[int]
:rtype: TreeNode
"""
length = len(nums)
if length == 0:
return None
if length == 1:
return TreeNode(nums[0])
if length == 2:
root = TreeNode(nums[0])
root.right = TreeNode(nums[1])
if length == 3:
root = TreeNode(nums[1])
root.left = TreeNode(nums[0])
root.right = TreeNode(nums[2])
return root
root = TreeNode(nums[length / 2])
root.left = self.sortedArrayToBST(nums[:length / 2])
root.right = self.sortedArrayToBST(nums[length / 2 + 1:])
return root