> ## Documentation Index
> Fetch the complete documentation index at: https://leetcode-py.wisl.dev/llms.txt
> Use this file to discover all available pages before exploring further.

> ## Agent Instructions
> leetcode-py is a Python LeetCode practice environment generator with one CLI: lcpy. It is not a service or platform.
> Each problem is a directory under leetcode/ with README.md, solution.py, test_solution.py, helpers.py, and playground.ipynb. lcpy gen creates them from JSON templates bundled with the package.
> Examples are backed by tests; copy them verbatim.

# Balanced Binary Tree Python Solution

> Tested Python solution for LeetCode 110 with 15 pytest cases. Generate a practice environment with lcpy.

LeetCode 110, Easy. Topics: Tree, Depth-First Search, Binary Tree. [View on LeetCode](https://leetcode.com/problems/balanced-binary-tree/description/).

Generate this problem as a practice environment: tested reference solution, 15 [parametrized pytest cases](/practice/testing), and a playground notebook:

```bash theme={"theme":{"light":"github-light","dark":"github-dark"}}
lcpy gen -n 110   # by problem number
lcpy gen -s balanced_binary_tree   # by problem name
```

## Problem

Given a binary tree, determine if it is **height-balanced**.

A height-balanced binary tree is a binary tree in which the depth of the two subtrees of every node never differs by more than one.

### Examples

![Example 1](https://assets.leetcode.com/uploads/2020/10/06/balance_1.jpg)

```
Input: root = [3,9,20,null,null,15,7]
Output: true
```

![Example 2](https://assets.leetcode.com/uploads/2020/10/06/balance_2.jpg)

```
Input: root = [1,2,2,3,3,null,null,4,4]
Output: false
```

```
Input: root = []
Output: true
```

### Constraints

* The number of nodes in the tree is in the range `[0, 5000]`.
* `-10^4 <= Node.val <= 10^4`

## Solution

Reference implementation from [solution.py on GitHub](https://github.com/wislertt/leetcode-py/blob/main/leetcode/balanced_binary_tree/solution.py), full suite in [test\_solution.py](https://github.com/wislertt/leetcode-py/blob/main/leetcode/balanced_binary_tree/test_solution.py):

```python theme={"theme":{"light":"github-light","dark":"github-dark"}}
from leetcode_py import TreeNode


class Solution:
    # Time: O(n)
    # Space: O(h)
    def is_balanced(self, root: TreeNode[int] | None) -> bool:
        def height(node: TreeNode[int] | None) -> int:
            if not node:
                return 0

            left = height(node.left)
            right = height(node.right)

            if left == -1 or right == -1 or abs(left - right) > 1:
                return -1

            return max(left, right) + 1

        return height(root) != -1
```

## Complexity

| Time | Space |
| ---- | ----- |
| O(n) | O(h)  |

## Tags

[Grind 75](/catalog/grind-75), [Grind](/catalog/grind), [NeetCode 150](/catalog/neetcode-150), [NeetCode 250](/catalog/neetcode-250), [NeetCode All](/catalog/neetcode).