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Goldman Sachs·Software Engineer·Technical Phone Screen·Intermediate

Intermediate
Jun 2026

Summary

Goldman Sachs software engineer interview with a coding question around simulating robot movement on a grid, plus a follow-up on design extensibility. Pretty straightforward technically but the second part tripped me up a bit.

Questions Asked (2)

Q1

Given a string of direction commands like 'U', 'D', 'L', 'R', simulate a robot moving on a 2D grid using a switch/case dispatch and return the final position or full path.

Algorithms & Data Structures
Author's notes

The core part was fine.

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AI HintsAI Generated

Suggested Approach

Start by clarifying the problem requirements, such as whether to return the final position or the full path, and the coordinate system. Then, outline a solution using a switch/case statement to update the position based on each command, and discuss how to handle edge cases and optimize if needed.

Pro tip: Mention that while a switch/case is straightforward, using a hashmap for direction deltas can be more concise and scalable, but be prepared to implement either as requested. Also, consider discussing time and space complexity upfront to demonstrate efficiency awareness.

1. Clarify Requirements

Ask about the coordinate system (e.g., origin at (0,0), U increases y, etc.), whether to return final position or full path, and if the grid has boundaries.

2. Design the Algorithm

Initialize position variables and a path list if needed. Iterate through each character in the string, using a switch/case to update the position accordingly.

3. Implement the Solution

Write clean code with a switch statement for each direction, updating x and y. If tracking path, append the new position after each move.

4. Test and Validate

Walk through examples, including edge cases like empty string, invalid characters, and large inputs. Verify the output matches expectations.

5. Analyze Complexity

State that time complexity is O(n) for n commands, and space complexity is O(1) for final position or O(n) if storing the full path.

Key Points to Mention

  • Coordinate system definition: specify that U increases y, D decreases y, L decreases x, R increases x, with starting point at (0,0).
  • Use of switch/case for clarity and efficiency, but note that a hashmap of direction deltas is an alternative.
  • Handling invalid characters: either ignore them or throw an error, depending on requirements.
  • Tracking the full path: maintain a list of positions and append after each move.
  • Time and space complexity analysis: O(n) time, O(1) or O(n) space depending on output.
  • Edge cases: empty string, single command, commands that cancel out, and potential integer overflow for very long strings.

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

Q2

How would you handle mixed-case input like 'u' or 'l' alongside uppercase commands, and how would you redesign to support more commands without expanding a giant switch statement?

Technical Trade-offsSystem Design
Author's notes

Normalizing case was trivial, just toUpperCase before dispatch, no issue there.

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AI HintsAI Generated

Suggested Approach

Start by normalizing input (e.g., lowercasing) to handle mixed-case commands, then discuss replacing the switch statement with a command pattern or a map of command handlers. Emphasize extensibility, maintainability, and testability as key drivers for the redesign.

Pro tip: Mention that normalizing input at the boundary (e.g., in the parser) keeps the core logic clean and avoids scattering case-handling throughout the code. Also, highlight that using a registry pattern allows adding new commands without modifying existing code, adhering to the Open/Closed Principle.

1. Clarify Requirements and Constraints

Ask about the expected input format, performance requirements, and whether commands might have different case-sensitivity rules. This shows you consider context before jumping to solutions.

2. Normalize Input

Propose converting input to a consistent case (e.g., lowercase) early in the processing pipeline, such as during parsing or tokenization, to simplify command matching.

3. Refactor Switch to Command Pattern

Replace the switch statement with a command pattern: define a Command interface, implement concrete commands, and use a factory or registry to map command names to handlers.

4. Implement a Command Registry

Use a map (e.g., dictionary) to associate normalized command strings with command objects or functions, allowing dynamic registration of new commands without modifying existing code.

5. Discuss Trade-offs and Extensibility

Compare the switch approach (simple but rigid) with the command pattern (more classes but extensible). Mention how this design supports adding commands via configuration or plugins.

Key Points to Mention

  • Input normalization (e.g., lowercasing) at the boundary to handle mixed-case input consistently.
  • Command pattern or strategy pattern to encapsulate each command as an object.
  • Registry or map-based dispatch to avoid switch statements and enable easy addition of new commands.
  • Open/Closed Principle: classes should be open for extension but closed for modification.
  • Testability: each command can be unit tested independently.
  • Performance considerations: map lookup is O(1) vs. switch which may be compiled to jump table; but maintainability often outweighs micro-optimizations.

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