Invert Binary Tree – Solution & Complexity
1. Recognize the Pattern
The key pattern is: DFS swaps children at every node. Identify the state and invariant before coding.
2. Build the Algorithm
Advance one state transition at a time. Mark or update state before exploring dependent work.
3. Check Edge Cases
Test empty or minimal input, skewed shapes, duplicates where allowed, and impossible outcomes.
4. Solution and Complexity
Time: O(n). Space: O(h).
