Microsoft·Software Engineer·Technical Phone Screen·Intermediate

Intermediate

May 2026

Summary

Microsoft SWE interview with a grid-based coding problem that builds on the classic connected components setup but adds a classification layer. Pretty straightforward if you've done flood fill before, but the thunderstorm condition trips you up if you're not careful about the math.

Questions Asked (1)

Given a 2D grid of heat radiation values, cells with index 4 or below form 'clouds' connected in 4 directions. For each cloud, determine if it's a 'thunderstorm' cloud, meaning at least half its cells have a heat radiation index of 1 or below. Return whether any such thunderstorm cloud exists, or a count of them.

Algorithms & Data StructuresTechnical Trade-offs

Author's notes

I did the BFS for connected components fine, that part felt routine.

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AI HintsAI Generated

Suggested Approach

Model the grid as a graph and use BFS/DFS to find connected components of cells with value ≤4. For each component, count cells with value ≤1 and check if that count is at least half the component size. Return true if any such component exists, or the total count.

Pro tip: Clarify with the interviewer whether to return a boolean or a count, and discuss trade-offs between BFS and DFS (e.g., recursion depth vs. queue memory). Also, mention edge cases like empty grid or no clouds.

1. Clarify requirements and edge cases

Confirm whether the output should be a boolean or a count, and discuss handling of empty grids, single-cell clouds, and cells with value exactly 4 or 1.

2. Choose traversal method

Decide between BFS (iterative, queue) and DFS (recursive or stack) for finding connected components. Consider memory and recursion limits.

3. Implement component traversal

Iterate through each cell; if unvisited and value ≤4, start BFS/DFS to explore the cloud, marking visited cells and counting total cells and cells with value ≤1.

4. Evaluate thunderstorm condition

For each cloud, check if the count of low-value cells is at least half the total cells. If so, it's a thunderstorm cloud.

5. Return result

If any thunderstorm cloud is found, return true (or increment a counter). After processing all clouds, return the final boolean or count.

Key Points to Mention

Connected components in a grid using 4-directional adjacency
BFS vs DFS trade-offs: iterative BFS avoids recursion depth issues; DFS may be simpler but risks stack overflow
Time complexity O(R*C) and space complexity O(R*C) for visited tracking
In-place modification of the grid to mark visited cells (if allowed) to save space
Handling edge cases: empty grid, no clouds, clouds with exactly half low-value cells
Clarifying output format: boolean existence vs. count of thunderstorm clouds

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