> For the complete documentation index, see [llms.txt](https://imhuay.gitbook.io/studies/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://imhuay.gitbook.io/studies/algorithms/problems/2022/01/niu-ke-0011-jian-dan-jiang-sheng-xu-shu-zu-zhuan-hua-wei-ping-heng-er-cha-sou-suo-shu.md).

# 将升序数组转化为平衡二叉搜索树

![last modify](https://img.shields.io/static/v1?label=last%20modify\&message=2022-10-14%2014%3A59%3A33\&color=yellowgreen\&style=flat-square) [![](https://img.shields.io/static/v1?label=\&message=%E7%AE%80%E5%8D%95\&color=yellow\&style=flat-square)](https://imhuay.gitbook.io/studies/algorithms/problems/2022/01/pages/R5NyOzkn3qAZy7wCx1pS#简单) [![](https://img.shields.io/static/v1?label=\&message=%E7%89%9B%E5%AE%A2\&color=green\&style=flat-square)](https://imhuay.gitbook.io/studies/algorithms/problems/2022/01/pages/R5NyOzkn3qAZy7wCx1pS#牛客) [![](https://img.shields.io/static/v1?label=\&message=%E4%BA%8C%E5%8F%89%E6%A0%91/%E6%A0%91\&color=blue\&style=flat-square)](https://imhuay.gitbook.io/studies/algorithms/problems/2022/01/pages/R5NyOzkn3qAZy7wCx1pS#二叉树树)

**问题简述**

```
给定升序数组，转化为平衡二叉搜索树（BST）
```

> [将升序数组转化为平衡二叉搜索树\_牛客题霸\_牛客网](https://www.nowcoder.com/practice/7e5b00f94b254da599a9472fe5ab283d)

**思路**

* 每次选择中间节点作为根节点，按先序遍历递归构建 BST；

<details>

<summary><strong>Python</strong></summary>

```python
# class TreeNode:
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None
#
# 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
#
# 
# @param num int整型一维数组 
# @return TreeNode类
#
class Solution:
    def sortedArrayToBST(self , num: List[int]) -> TreeNode:
        # write code here
        def dfs(arr):
            if not arr: return None
            
            l, r = 0, len(arr) - 1
            mid = (l + r) // 2
            
            node = TreeNode(arr[mid])
            node.left = dfs(arr[:mid])
            node.right = dfs(arr[mid + 1:])
            
            return node
        
        return dfs(num)
```

</details>


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