The thing that tripped me up first was state modeling.
Start by clarifying requirements and constraints, then outline a component architecture with a clear data model for the board and ships. Focus on state management, efficient updates, and deriving sunk status, while discussing trade-offs and edge cases.
Pro tip: Demonstrate production thinking by discussing memoization to prevent unnecessary re-renders of the grid and using a normalized state structure for O(1) ship lookups.
Ask about board size, ship configurations, cell state cycle order, and whether the status panel should update in real-time. Confirm if any persistence or reset functionality is needed.
Define a 2D array for cell states (e.g., empty, ship, hit, miss) and a separate structure for ships with their coordinates and sunk status. Consider using a Map for ship lookup by cell.
Break down into Board, Cell, and StatusPanel components. Decide where state lives (likely in a parent Board component) and how to pass down handlers efficiently.
Use immutable updates for cell state changes. On click, cycle the cell state and check if any ship becomes fully hit, updating its sunk status accordingly.
Memoize Cell components to avoid re-renders. Discuss trade-offs between storing derived state vs. computing on the fly, and between using a single state object vs. multiple useState hooks.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.
I went with a single parent owning all state and passing down props.
Start by clarifying the requirements and constraints of the grid and ship status panel, such as real-time updates, performance needs, and component reusability. Then propose a component hierarchy that separates presentational and container components, and discuss where state should live based on ownership and update frequency. Finally, justify your choices with trade-offs around performance, maintainability, and scalability.
Pro tip: Emphasize that state should be lifted to the closest common ancestor only when necessary, and consider using React context or a state management library for global state like ship status if it's shared across many components. Also, mention memoization techniques to prevent unnecessary re-renders in the grid.
Ask about the grid's size, update frequency, and interactivity, and the ship status panel's data sources and update rate. This ensures your design meets actual needs.
Break down the UI into components: a Grid container, GridCell components, a ShipStatusPanel, and possibly a shared parent. Decide which components are presentational vs. container.
Identify what state is needed (e.g., grid data, ship status) and where it should live. Lift state to the closest common ancestor if shared, or keep it local if only one component needs it.
Discuss strategies like React.memo, useCallback, and virtualization for the grid to handle frequent updates efficiently. Consider using context or Redux for global state if needed.
Explain the pros and cons of your choices, such as prop drilling vs. context, local state vs. global state, and how they affect maintainability and performance.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.
Start by clarifying the scenario: is this a React component, vanilla JS, or another framework? Then explain how you ensure state updates are based on the latest state, not stale closures, by using functional updates or refs. Finally, discuss how you handle rapid clicks to avoid race conditions, such as batching or debouncing, and how you verify correctness with tests.
Pro tip: Mention that in React, using the functional form of setState (e.g., setCellState(prev => ...)) avoids stale state issues, but if you need the absolute latest value synchronously, a ref can be used. Also, note that React 18's automatic batching can affect timing, so be explicit about your assumptions.
Ask or state the framework (React, Vue, vanilla JS) and whether the cell state is local or global. This determines the tools available (e.g., hooks, refs, event delegation).
Describe how rapid clicks can cause multiple handlers to read the same outdated state value, leading to lost updates. This shows you understand the core issue.
Detail how you use functional updates (e.g., setState(prev => ...)) or a ref to always operate on the latest state. If using a ref, explain how you keep it in sync.
Discuss strategies like debouncing, throttling, or disabling the button during processing to prevent race conditions. Mention if you rely on framework batching or event loop behavior.
Explain how you would test this scenario, such as with unit tests simulating rapid clicks or using React Testing Library's fireEvent. Mention edge cases like double-click or async updates.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.
Reset was easy since sunk status is derived.
Start by clarifying the game rules and expected behavior for each edge case, then propose a state management strategy that handles them deterministically. Emphasize defensive programming, clear state transitions, and testability, while acknowledging trade-offs between simplicity and robustness.
Pro tip: Mention that you'd write unit tests for these edge cases first (TDD) to ensure they're handled correctly and to document expected behavior. This shows maturity and a proactive approach to quality.
Ask questions to understand the exact rules: Can ships overlap? What should happen on repeated clicks? Is reset expected to clear all state? This ensures you're solving the right problem.
Propose a state representation that prevents invalid states, such as a 2D array for the board and a separate structure for ship positions. Use immutable updates to avoid side effects.
For overlapping ships, validate placement before committing. For repeated clicks, cycle through states (empty -> ship -> hit -> empty) or prevent invalid transitions. For reset, reinitialize state to initial values.
Write unit tests for each edge case to verify behavior. Use a testing library like Jest to simulate clicks and assert state changes.
Acknowledge trade-offs: e.g., allowing overlapping ships simplifies placement but may complicate hit detection. Choose based on game requirements and user experience.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.
Mentioned virtualization for rendering and switching from a full-scan sunk check to an incremental counter per ship updated on each click.
Start by clarifying the current rendering and sunk-detection implementation, then identify bottlenecks at 1000x1000 scale. Propose a combination of spatial partitioning, level-of-detail rendering, and optimized data structures, while discussing trade-offs between accuracy and performance.
Pro tip: Mention that sunk-detection can be approximated using a coarse grid or bounding volumes, and only refined for cells near the water surface, showing you understand how to balance precision with performance.
Ask about the existing rendering technique (e.g., canvas, WebGL) and sunk-detection algorithm to understand what needs optimization. Confirm the grid size and performance targets.
Analyze where the performance issues would arise: number of draw calls, memory usage, detection complexity. Consider both rendering and detection separately.
Suggest techniques like spatial partitioning (quadtree), frustum culling, level-of-detail (LOD), and batching to reduce draw calls and only render visible cells.
Recommend using a coarse grid for broad-phase detection, then refine only near boundaries. Use spatial hashing or bounding volume hierarchies to reduce checks.
Acknowledge trade-offs between accuracy and performance, and suggest profiling and incremental improvements. Mention potential use of Web Workers for offloading detection.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.
Pure unit tests for the cycling logic and sunk detection since those are just functions.
Start by clarifying the component's responsibilities and dependencies, then propose a testing strategy that balances speed and confidence. Explain which parts are pure logic (unit tests) and which require rendering (component tests), justifying each choice with trade-offs.
Pro tip: Emphasize that unit tests should cover pure functions and business logic, while component tests should focus on user interactions and integration with child components. Mention that avoiding over-testing implementation details keeps tests maintainable.
Ask questions to understand the component's purpose, props, state, and external dependencies (e.g., APIs, context). This ensures your testing strategy is tailored to its actual behavior.
List parts that are pure functions, utilities, or state reducers that can be tested in isolation without rendering. These are ideal for fast unit tests.
Determine which parts involve rendering, user events, or integration with child components. These require component tests using a library like React Testing Library.
For each category, outline specific test cases: unit tests for edge cases and logic branches; component tests for rendering output, user interactions, and conditional rendering.
Explain why you split tests this way, mentioning speed, reliability, and maintenance. Acknowledge that some overlap is okay but avoid redundant tests.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.