> ## 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.

# Diameter of Binary Tree Python Solution

> Tested Python solution for LeetCode 543 with 12 pytest cases. Generate a practice environment with lcpy.

LeetCode 543, Easy. Topics: Tree, Depth-First Search, Binary Tree. [View on LeetCode](https://leetcode.com/problems/diameter-of-binary-tree/description/).

Generate this problem as a practice environment: tested reference solution, 12 [parametrized pytest cases](/practice/testing), and a playground notebook:

```bash theme={"theme":{"light":"github-light","dark":"github-dark"}}
lcpy gen -n 543   # by problem number
lcpy gen -s diameter_of_binary_tree   # by problem name
```

## Problem

Given the `root` of a binary tree, return the length of the **diameter** of the tree.

The **diameter** of a binary tree is the **length** of the longest path between any two nodes in a tree. This path may or may not pass through the `root`.

The **length** of a path between two nodes is represented by the number of edges between them.

### Examples

![Example 1](https://assets.leetcode.com/uploads/2021/03/06/diamtree.jpg)

```
Input: root = [1,2,3,4,5]
Output: 3
```

**Explanation:** 3 is the length of the path \[4,2,1,3] or \[5,2,1,3].

```
Input: root = [1,2]
Output: 1
```

### Constraints

* The number of nodes in the tree is in the range \[1, 10^4].
* -100 \<= Node.val \<= 100

## Solution

Reference implementation from [solution.py on GitHub](https://github.com/wislertt/leetcode-py/blob/main/leetcode/diameter_of_binary_tree/solution.py), full suite in [test\_solution.py](https://github.com/wislertt/leetcode-py/blob/main/leetcode/diameter_of_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 diameter_of_binary_tree(self, root: TreeNode[int] | None) -> int:
        self.max_diameter = 0

        def dfs(node: TreeNode[int] | None) -> int:
            if not node:
                return 0

            left = dfs(node.left)
            right = dfs(node.right)

            self.max_diameter = max(self.max_diameter, left + right)

            return max(left, right) + 1

        dfs(root)
        return self.max_diameter
```

## 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).