Solve the Easy-level Invert Binary Tree coding interview problem online in Python & JavaScript. Run your code against real test cases in the browser and study worked examples. It covers binary tree, depth first search, and recursion. Read the step-by-step solution and complexity analysis. Java starter code is also included for reference (no in-browser JVM yet, so it can't be run here).

Invert Binary Tree – Solve Online in Python & JavaScript

Same Tree

Subsets

Swap every binary-tree node's left and right children.

Given the root of a binary tree, invert it in place and return the root.

## Example
```json
Input: {"root":[4,2,7,1,3,6,9]}
Output: [4,7,2,9,6,3,1]
```

## Constraints
- 0 <= number of nodes <= 1000
- -100 <= node value <= 100

## Follow-up
Can you implement both recursive DFS and iterative BFS?

## Execution note
Java/Go/Rust don't support this problem's ListNode/TreeNode structure yet — the starter is reference-only. Try Python or JavaScript to run and submit.

The key pattern is: DFS swaps children at every node. Identify the state and invariant before coding.

Recognize the Pattern

Advance one state transition at a time. Mark or update state before exploring dependent work.

Build the Algorithm

Test empty or minimal input, skewed shapes, duplicates where allowed, and impossible outcomes.