rippling·Software Engineer·Technical Phone Screen·Senior

Senior

Apr 2026

Summary

Rippling full-stack interview with a grid/matrix problem that looked like a BFS warmup but had enough edge cases to keep you honest. The jagged row thing specifically tripped me up more than I expected.

Questions Asked (1)

Given a jagged matrix where rows can have different lengths and cells are either 1 or empty, find all maximally connected regions of 1s using 4-directional adjacency. For each connected region, return the bounding box coordinates in a column-letter/row-number format (like A2 or B3).

Algorithms & Data StructuresTechnical Trade-offs

Author's notes

I went straight to BFS for connected components which was fine, but the bounding box part slowed me down.

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AI HintsAI Generated

Suggested Approach

Clarify the problem constraints and edge cases, then propose a BFS/DFS solution that traverses each cell once, tracking visited cells and updating bounding box coordinates for each connected component. Finally, convert the bounding box coordinates to the required column-letter/row-number format.

Pro tip: Discuss how to handle very large matrices by streaming rows or using union-find, and mention the trade-offs between BFS and DFS in terms of memory and recursion depth.

1. Clarify requirements and constraints

Ask about matrix size, memory limits, and whether the matrix is static or dynamic. Confirm the coordinate format and that regions are maximal (cannot be extended).

2. Choose traversal algorithm

Select BFS or DFS for 4-directional connectivity. BFS is iterative and avoids recursion limits; DFS is simpler but may risk stack overflow on large regions.

3. Track visited cells and bounding boxes

Use a visited set or modify the matrix in-place. For each unvisited '1', start a traversal, updating min/max row and column indices for the current region.

4. Convert coordinates to required format

Convert the bounding box's top-left and bottom-right coordinates to column-letter/row-number format (e.g., A2). Ensure correct handling of multi-letter columns (e.g., AA).

5. Analyze complexity and trade-offs

State time complexity O(N) where N is total cells, and space complexity O(N) for visited set or O(1) if in-place. Discuss trade-offs between BFS/DFS and potential optimizations.

Key Points to Mention

4-directional adjacency (up, down, left, right) and how it defines connectivity.
Handling jagged rows: ensure column indices are valid for each row during traversal.
Bounding box definition: min/max row and column indices of the region.
Coordinate conversion: mapping 0-based indices to column letters (A=0, B=1, ..., Z=25, AA=26, etc.) and row numbers (1-based).
Edge cases: empty matrix, no 1s, single cell, regions touching matrix borders.
Complexity analysis: O(R*C) time, O(R*C) space for visited set (or O(1) if in-place).

AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.