My first instinct was to just replay all transactions up to the timestamp on every call, which works but is obviously slow.
Start by clarifying requirements such as consistency, latency, and data volume, then propose an append-only ledger with timestamped entries. For efficient queries, suggest a time-series data structure like a segment tree or balanced BST, and discuss trade-offs between in-memory and persistent storage.
Pro tip: Mention that you would use a combination of a write-ahead log for durability and an in-memory index for fast queries, and highlight the importance of handling concurrent writes and reads with appropriate locking or MVCC.
Ask about expected query patterns, data retention, consistency needs, and performance SLAs to scope the design appropriately.
Propose an append-only ledger where each transaction is stored with a timestamp, and consider using a time-series database or a custom index.
Select a data structure that supports efficient range queries and point lookups, such as a segment tree, Fenwick tree, or balanced BST, and explain how it enables O(log n) queries.
Specify the GET_BALANCE_AT endpoint with parameters like account ID and timestamp, and define the response format including balance and currency.
Discuss partitioning, replication, and consistency models (e.g., eventual vs. strong) to ensure the system scales and meets correctness requirements.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.