> ## 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.

# Inorder Successor in BST Python Solution

> Tested Python solution for LeetCode 285 with 16 pytest cases. Generate a practice environment with lcpy.

LeetCode 285, Medium. Topics: Tree, Depth-First Search, Binary Search Tree, Binary Tree. [View on LeetCode](https://leetcode.com/problems/inorder-successor-in-bst/description/).

Generate this problem as a practice environment: tested reference solution, 16 [parametrized pytest cases](/practice/testing), and a playground notebook:

```bash theme={"theme":{"light":"github-light","dark":"github-dark"}}
lcpy gen -n 285   # by problem number
lcpy gen -s inorder_successor_in_bst   # by problem name
```

## Problem

Given the `root` of a binary search tree and a node `p` in it, return *the in-order successor of that node in the BST*. If the given node has no in-order successor in the tree, return `null`.

The successor of a node `p` is the node with the smallest key greater than `p.val`.

### Examples

```
Input: root = [2,1,3], p = 1
Output: 2
Explanation: 1's in-order successor node is 2. Note that both p and the return value are of TreeNode type.
```

```
Input: root = [5,3,6,2,4,null,null,1], p = 6
Output: null
Explanation: There is no in-order successor of the current node, so the answer is null.
```

### Constraints

* The number of nodes in the tree is in the range `[1, 10^4]`.
* `-10^5 <= Node.val <= 10^5`
* All Nodes will have unique values.

## Solution

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

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


class Solution:
    # Time: O(h)
    # Space: O(1)
    def inorder_successor(
        self, root: TreeNode[int] | None, p: TreeNode[int]
    ) -> TreeNode[int] | None:
        # If p has a right subtree, successor is leftmost node of that subtree.
        # Otherwise, successor is the lowest ancestor for which p lies in its
        # left subtree. Track candidate successor while walking down.
        successor = None
        while root:
            if p.val < root.val:
                successor = root
                root = root.left
            else:
                root = root.right
        return successor
```

## Complexity

| Time | Space |
| ---- | ----- |
| O(h) | O(1)  |

## Tags

[Grind](/catalog/grind).