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.
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?