Check whether every node’s left and right subtree heights differ by at most one.
A good solution should
- State the invariant or decision rule that makes the approach correct.
- Explain the time and space complexity in terms of the input sizes and required output.
- Handle empty, minimal, duplicate, and boundary-shaped inputs covered by the contract.
Reasoning prompt
Avoid recomputing subtree height at every node. Return either height or an imbalance marker in one postorder pass.
Use the linked judge for the canonical problem. The examples above are compact TRT checks; write additional cases before submitting, especially for the boundary that tends to break your chosen invariant.