Figma·Machine Learning Engineer·Technical Phone Screen·Senior

Senior

Jul 2026

Summary

Figma ML engineer screen, one coding problem the whole time. Pretty standard graph traversal territory but they wanted you to actually talk through the tradeoffs between approaches rather than just code it up.

Questions Asked (1)

Given a 2D grid where cells are either land or water, count the number of distinct islands, where an island is any group of land cells connected horizontally or vertically.

Algorithms & Data StructuresTechnical Trade-offs

Author's notes

I went with DFS immediately which was fine, but they pushed me on why not BFS or union-find.

Create a free account to read the full note

AI HintsAI Generated

Suggested Approach

Clarify the problem constraints (grid size, connectivity definition) and then present a solution using either BFS/DFS or Union-Find to count connected components of land. Discuss trade-offs between approaches, including time/space complexity and potential optimizations for large grids.

Pro tip: Mention that you can avoid modifying the input by using a separate visited set, but if modification is allowed, marking visited cells in-place saves space. Also, relate this to real-world ML tasks like connected component labeling in image segmentation.

1. Clarify the problem

Ask about grid dimensions, whether diagonal connections count, and if the grid can be modified. Confirm that an island is a 4-directionally connected component of land cells.

2. Choose an algorithm

Decide between BFS/DFS (simpler, O(mn) time) and Union-Find (good for dynamic connectivity). Explain why BFS/DFS is typically preferred for this static problem.

3. Outline the approach

Iterate through each cell; when encountering unvisited land, increment island count and use BFS/DFS to mark all connected land cells as visited.

4. Analyze complexity

State time complexity O(mn) and space complexity O(mn) in worst case (e.g., all land). Mention that space can be O(min(m,n)) with BFS if using a queue, but worst-case still O(mn).

5. Discuss trade-offs and edge cases

Compare BFS vs DFS (stack overflow risk with DFS on large grids). Mention edge cases: empty grid, all water, all land, and single row/column.

Key Points to Mention

Time and space complexity analysis for BFS/DFS and Union-Find.
In-place modification vs using a visited set.
Handling edge cases like empty grid or no land.
Potential for parallelization or optimization for very large grids.
Connection to ML applications (e.g., connected component labeling in image segmentation).
Trade-offs between BFS and DFS (e.g., recursion depth, queue memory).

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