Start by clarifying the problem constraints and edge cases, then propose a two-phase solution: first scan the grid to identify all runs of length >= 3, then mark those cells for removal and apply gravity column-wise. Discuss time/space complexity and potential optimizations, such as using a visited array or processing runs in a single pass.
Pro tip: Mention that you would handle overlapping runs carefully—a cell can belong to both a horizontal and vertical run—and ensure it's only removed once. Also, consider using a boolean matrix to mark removed cells to avoid modifying the grid during the scan.
Ask about grid size limits, whether runs can overlap, and if the output should be sorted as specified. Confirm that after removal, digits fall down and zeros fill the top.
Scan each row for horizontal runs and each column for vertical runs of the same digit with length >= 3. Record each run as [row, col, length] and sort them as required.
Use a boolean matrix to mark all cells that belong to any identified run. This handles overlaps and ensures each cell is removed only once.
For each column, collect the remaining digits from bottom to top, then place them at the bottom of the column and fill the top with zeros.
Discuss time complexity O(m*n) for scanning and gravity, and space complexity O(m*n) for the boolean matrix. Mention potential optimizations like in-place marking or using a queue for runs.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.