Count connected land regions in a grid where horizontal and vertical neighbors connect.
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
Start a traversal at each unvisited land cell and mark its full component. Avoid changing input if callers depend on preserving the grid.
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.