Simulate a Bank Application | Dataford Interview Questions

Build a software application simulating a bank.

Implement simulate_bank(operations), which processes operations in order while maintaining account balances. Support account creation, deposits, withdrawals, transfers, and balance queries. Deposits, withdrawals, and transfers include unique transaction IDs and must be idempotent: repeating an ID returns the original result without changing state. Transfers must be atomic, so insufficient funds or invalid accounts leave both balances unchanged.

Contract

Input is a list of operation dictionaries. Return one result dictionary per operation. Amounts are nonnegative integer cents. Use {"ok": true} for successful mutations, include balance for balance queries and successful deposits or withdrawals, and use {"ok": false, "error": "..."} for rejected operations. Use the exact operation shapes shown in the examples.

Constraints

1 <= operations.length <= 200000
Account identifiers are nonempty strings
Amounts and initial balances are integers in the range 0 through 10^12
Every DEPOSIT, WITHDRAW, and TRANSFER operation contains a unique transaction ID unless it is an intentional retry
Transaction IDs are strings
Operations are processed strictly in input order

Function Signature

def simulate_bank(operations):

Your question is Simulate a Bank Application. Start with the requirements in the Question tab.

Run and submit as often as you like. When you're ready, talk me through your approach or go straight to the code.

Problem