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Google·Software Engineer·Onsite - Coding / Algorithms·Senior

SeniorPrefer not to say
Jun 2026

Summary

Google SWE interview with a grid layout problem that started familiar and then got weird fast. The shape twist caught me off guard more than I expected for what looked like a coding round.

Questions Asked (3)

Q1

Given an irregular garden shape formed by two squares of different sizes stacked vertically and left-aligned (total area N² + M²), and a list of crop types with prescribed cell counts summing to the total area, generate a planting layout where each crop type occupies exactly its prescribed number of cells and forms a single 4-connected region.

Algorithms & Data StructuresTechnical Trade-offs
Author's notes

My first instinct was to just run a boustrophedon traversal like you would on a plain rectangle, assign crops in order, done.

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AI HintsAI Generated

Suggested Approach

Model the garden as a grid graph where each cell is a node and edges connect 4-adjacent cells. The problem reduces to partitioning this graph into connected subgraphs of given sizes, which is NP-hard in general; therefore, propose a constructive heuristic or backtracking search that assigns crops sequentially while maintaining connectivity. Discuss trade-offs between optimality, runtime, and implementation complexity, and consider special structure of the shape (two stacked squares) to simplify partitioning.

Pro tip: Emphasize that perfect solutions may be intractable, so a practical approach is to use a greedy region-growing algorithm with backtracking, and validate connectivity with BFS/DFS. Mention that for Google-scale inputs, you'd also consider parallelization or approximation guarantees.

1. Understand the problem and constraints

Clarify that the garden is a union of two axis-aligned squares of sizes N×N and M×M, left-aligned and stacked vertically, forming an irregular shape. The total number of cells is N² + M², and each crop type must occupy exactly its prescribed count as a single 4-connected region.

2. Model as a graph partitioning problem

Represent each cell as a vertex in a grid graph, with edges between 4-adjacent cells. The goal is to partition the vertex set into connected components of specified sizes, which is a connected graph partitioning problem.

3. Choose an algorithmic strategy

Since the problem is NP-hard, propose a constructive heuristic: sort crops by size (largest first) and grow regions using BFS/DFS from seed cells, ensuring connectivity. Alternatively, use backtracking with pruning or integer programming for small instances.

4. Handle feasibility and edge cases

Check if a solution exists (e.g., if any crop size exceeds the largest connected component of remaining cells). Discuss how to handle cases where greedy fails, such as using local search or simulated annealing to repair connectivity.

5. Analyze complexity and trade-offs

Evaluate time/space complexity of the chosen approach, and discuss trade-offs between optimality, runtime, and implementation complexity. Mention that for large N and M, approximation or parallelization may be needed.

Key Points to Mention

  • Graph representation of the garden as a grid graph with 4-connectivity.
  • NP-hardness of connected graph partitioning, justifying heuristic or approximation approaches.
  • Greedy region-growing with BFS/DFS to ensure connectivity.
  • Backtracking or local search for repair when greedy fails.
  • Complexity analysis: O(total cells) for BFS, but exponential worst-case for backtracking.
  • Special structure of the shape (two stacked squares) could be exploited for simpler partitioning.

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

Q2

How does the irregular two-square shape change your traversal strategy compared to a standard rectangular garden, particularly at the seam where the two squares meet?

Algorithms & Data StructuresAdaptability & Ambiguity
Author's notes

Spent probably too long explaining why the snake traversal still works in theory before actually addressing where it breaks.

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AI HintsAI Generated

Suggested Approach

First, clarify the problem: define the irregular two-square shape (e.g., two squares sharing a full edge) and the traversal goal (e.g., visiting all cells, finding a path). Then, compare standard rectangular traversal (e.g., row-major) with the irregular shape, focusing on the seam where the squares meet, and propose an adapted strategy such as treating each square as a subgrid and handling the seam with special logic.

Pro tip: Demonstrate adaptability by acknowledging that real-world problems often have irregular constraints; mention that you would write unit tests specifically for the seam to ensure correctness, showing maturity in handling edge cases.

1. Clarify the problem

Ask clarifying questions to understand the exact shape (e.g., two squares sharing an edge, forming a rectangle or an L-shape) and the traversal goal (e.g., visit all cells, find a path, search).

2. Analyze the seam

Identify the seam where the two squares meet and how it affects adjacency and traversal order; note that the seam may create non-uniform neighbor relationships.

3. Adapt traversal strategy

Propose a strategy such as decomposing into two subgrids and traversing each with standard methods, then handling the seam with special logic to ensure continuity.

4. Consider edge cases

Discuss potential issues like double-counting cells at the seam, ensuring all cells are visited exactly once, and handling boundary conditions.

5. Evaluate and optimize

Compare the adapted strategy with a naive approach in terms of time and space complexity, and suggest optimizations if needed.

Key Points to Mention

  • Definition of the irregular shape: two squares sharing an edge, forming a rectangle or L-shape.
  • Standard rectangular traversal: row-major or column-major order, uniform neighbor relationships.
  • Seam challenges: non-uniform adjacency, potential for double-counting or missing cells.
  • Adapted strategy: decompose into subgrids, traverse each, then handle seam with special logic.
  • Edge cases: cells at the seam, boundary conditions, ensuring complete coverage.
  • Complexity analysis: time and space trade-offs of the adapted strategy.

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

Q3

Are all input multisets of crop counts feasible for this shape, or are there configurations that cannot be planted while keeping each crop as a single 4-connected region?

Algorithms & Data StructuresTechnical Trade-offs
Author's notes

Blanked a bit here.

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AI HintsAI Generated

Suggested Approach

First, clarify the problem: we need to determine if every multiset of crop counts can be arranged on the given shape such that each crop forms a single 4-connected region. Then, analyze the shape's structure (e.g., grid, holes, narrow passages) and identify constraints that might make some multisets infeasible, such as limited space or forced separation. Finally, provide a constructive argument or counterexample to support your conclusion.

Pro tip: Demonstrate algorithmic thinking by relating this to graph partitioning or planar embedding problems, and mention that feasibility often depends on the shape's topology and the number of crops relative to the shape's size.

1. Clarify the problem

Restate the question in your own words to ensure you understand the shape, the crop counts, and the 4-connected requirement. Ask clarifying questions if needed.

2. Analyze the shape

Examine the shape's geometry: is it a simple grid, does it have holes, bottlenecks, or narrow corridors? Identify features that could restrict how regions can be placed.

3. Identify necessary conditions

Determine conditions for feasibility, such as total cells equaling sum of crop counts, and that each crop's count must be at least 1 if present. Consider if the shape can be partitioned into connected regions of given sizes.

4. Look for counterexamples

Try to construct a multiset that cannot be planted. For example, if the shape is a narrow ring, placing two crops might force them to interleave, violating connectivity.

5. Conclude and generalize

State whether all multisets are feasible or not, and under what conditions. If not, describe the class of infeasible configurations and suggest an algorithm to check feasibility.

Key Points to Mention

  • The shape's topology (e.g., simply connected vs. with holes) affects feasibility.
  • The problem is related to graph partitioning and connected subgraph problems.
  • Necessary conditions: total cells = sum of counts, and each crop's count must be ≤ size of largest connected component if shape is disconnected.
  • Sufficient conditions may involve the shape being a tree or having no bottlenecks.
  • Counterexamples often arise when the shape forces regions to be separated by other crops.
  • Algorithmic approach: model as a constraint satisfaction problem or use flow/matching techniques.

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