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Design an Airbnb wallet with holds and payouts

AirbnbSoftware Engineer · Technical Screen
HardSoftware EngineerTechnical ScreenSystem Design

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This question evaluates a candidate's competency in designing financial transaction systems, covering double-entry append-only ledgers, holds/authorizations and captures, refunds and payouts, multi-currency FX conversion and rounding, idempotency, concurrency safety, and auditable reconciliation.

Design and implement an Airbnb-style wallet system. Requirements: (

  1. create user accounts and allow deposits; (
  2. support booking holds/authorizations and later captures at check-in; (
  3. allow hold release on cancellation; (
  4. process partial/full refunds; (
  5. pay out hosts after platform fees and taxes; (
  6. enforce spendable vs. total balance with no negative spendable balance; (
  7. support multi-currency balances with FX conversion and rounding rules; (
  8. ensure idempotent operations via client-supplied idempotency keys; (
  9. guarantee concurrency safety for duplicate or overlapping requests; (
  10. maintain an append-only auditable ledger and derive balances from it; (
  11. provide reconciliation to detect inconsistencies; (
  12. define persistence schema (tables or classes) and transaction isolation choices; (
  13. expose clear APIs/methods and include a minimal main() to run sample scenarios; (
  14. write unit tests for happy paths and edge cases (insufficient funds, expired holds, double-capture attempts, partial refunds, FX rate changes). Specify core classes (e.g., Wallet, Account, Transaction, Hold, Capture, Refund, Payout, LedgerEntry, FXConverter), their relationships, and method signatures, and analyze time/space complexity of critical operations.