Clarify Friendship Rules and Money-Transfer Semantics Before Choosing an Algorithm

Quick Overview

Clarify friendship and money-transfer requirements, separate graph reachability from accounting, and reason about a conditional implementation and invariants.

Clarify Friendship Rules and Money-Transfer Semantics Before Choosing an Algorithm

Company: Robinhood

Role: Software Engineer

Category: Software Engineering Fundamentals

Difficulty: medium

Interview Round: Onsite

Discuss how you would clarify and implement a coding task involving friendship relationships and money transfers. The relationship between friendship and transfer behavior is unspecified, so start by defining the missing requirements instead of assuming a particular graph problem or financial policy. ### Part 1 — Establish the Operation Contract Identify the inputs, operations, outputs, and error cases needed to turn the task into an executable specification. In particular, clarify whether friendship controls eligibility, identifies a route, or merely stores separate relationship data. #### What This Part Should Cover Distinguish several plausible interpretations and explain which missing answers change the algorithm. Do not claim that any one interpretation is required. ### Part 2 — Develop One Explicitly Hypothetical Design Choose one interpretation, label its rules as assumptions, and describe the state, algorithm, and invariants. Explain how the design would change if the friendship rule were different. #### What This Part Should Cover Connect relationship representation to the declared rule. If balances are modeled, explain value conservation and rejection without partial updates. If the task only asks for reachability, do not invent account settlement behavior. ### Constraints No friendship direction, balance model, allowed-transfer rule, optimization objective, concurrency model, or error policy is supplied. This is a specification-and-design exercise; it has no single expected numeric output or fixed executable API. ### Clarifying Questions - Are friendship edges directed, and may relationships change? - Does a transfer require direct friendship, any connecting path, or no relationship check? - Are we finding a path, recording a transfer, or updating account balances? - Are insufficient funds, duplicate requests, or concurrent operations in scope? ```hint Separate graph semantics from accounting A path in a friendship graph does not by itself define how money moves or which balances should change. ``` ### What a Strong Answer Covers - Explicit unresolved semantics and the consequences for algorithm selection. - A coherent hypothetical contract with well-defined state and failure behavior. - Complexity and validation appropriate to the chosen interpretation. ### Follow-up Questions - What changes if friendship can be removed while a transfer is being processed? - What information would you need before minimizing the number of transfers?

Overview: Clarify friendship and money-transfer requirements, separate graph reachability from accounting, and reason about a conditional implementation and invariants.

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Sep 11, 2026
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Discuss how you would clarify and implement a coding task involving friendship relationships and money transfers. The relationship between friendship and transfer behavior is unspecified, so start by defining the missing requirements instead of assuming a particular graph problem or financial policy.

Part 1 — Establish the Operation Contract

Identify the inputs, operations, outputs, and error cases needed to turn the task into an executable specification. In particular, clarify whether friendship controls eligibility, identifies a route, or merely stores separate relationship data.

What This Part Should Cover Guidance

Distinguish several plausible interpretations and explain which missing answers change the algorithm. Do not claim that any one interpretation is required.

Part 2 — Develop One Explicitly Hypothetical Design

Choose one interpretation, label its rules as assumptions, and describe the state, algorithm, and invariants. Explain how the design would change if the friendship rule were different.

What This Part Should Cover Guidance

Connect relationship representation to the declared rule. If balances are modeled, explain value conservation and rejection without partial updates. If the task only asks for reachability, do not invent account settlement behavior.

Constraints

No friendship direction, balance model, allowed-transfer rule, optimization objective, concurrency model, or error policy is supplied. This is a specification-and-design exercise; it has no single expected numeric output or fixed executable API.

Clarifying Questions Guidance

  • Are friendship edges directed, and may relationships change?
  • Does a transfer require direct friendship, any connecting path, or no relationship check?
  • Are we finding a path, recording a transfer, or updating account balances?
  • Are insufficient funds, duplicate requests, or concurrent operations in scope?

What a Strong Answer Covers Guidance

  • Explicit unresolved semantics and the consequences for algorithm selection.
  • A coherent hypothetical contract with well-defined state and failure behavior.
  • Complexity and validation appropriate to the chosen interpretation.

Follow-up Questions Guidance

  • What changes if friendship can be removed while a transfer is being processed?
  • What information would you need before minimizing the number of transfers?
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