leetcode108 Convert Sorted Array to Binary Search Tree

 1 """
 2 Given an array where elements are sorted in ascending order, convert it to a height balanced BST.
 3 For this problem, a height-balanced binary tree is defined as a binary tree in which the depth of the two subtrees of every node never differ by more than 1.
 4 Example:
 5 Given the sorted array: [-10,-3,0,5,9],
 6 One possible answer is: [0,-3,9,-10,null,5], which represents the following height balanced BST:
 7       0
 8      / 
 9    -3   9
10    /   /
11  -10  5
12 """
13 """
14 对于二叉搜索树，左右结点的值有规律，应该想到递归
15 二分+递归解法
16 """
17 class TreeNode:
18     def __init__(self, x):
19         self.val = x
20         self.left = None
21         self.right = None
22 
23 class Solution:
24     def sortedArrayToBST(self, nums):
25         return self.convert(nums, 0, len(nums) - 1)
26 
27     def convert(self, nums, left, right):
28         if left > right:  # bug 没写这个判断maximum recursion depth exceeded
29             return None
30         mid = (left + right) // 2
31         Node = TreeNode(nums[mid])
32         Node.left = self.convert(nums, left, mid - 1)
33         Node.right = self.convert(nums, mid + 1, right)
34         return Node