Implement deposit, withdraw, and transfer in a class
Company: Capital One
Role: Software Engineer
Category: Coding & Algorithms
Difficulty: medium
Interview Round: Onsite
## Problem
Implement a class `AccountService` that supports basic money operations on accounts.
### Operations
- `deposit(accountId, amount)`
- `withdraw(accountId, amount)`
- `transfer(fromAccountId, toAccountId, amount)`
- `getBalance(accountId)`
### Rules
- `amount` is a positive integer.
- `withdraw` must fail (return `false` or throw) if the account has insufficient funds.
- `transfer` must be **atomic**: either both balances change, or neither changes.
- If an account does not exist, treat its initial balance as 0 (or explicitly create on first use).
### Concurrency (if discussed)
Assume these methods may be called concurrently from multiple threads. Make the implementation thread-safe and avoid deadlocks.
### Input/Output
This is an in-memory class design question; you do not need to build a database or persistence.
Quick Answer: This question evaluates a candidate's competence in concurrent programming, atomic state updates, and class-level account management for basic monetary operations.
You are asked to model an in-memory `AccountService` that supports basic money operations. To make the class-design problem executable in a coding interview, implement a function `solution(operations)` that processes a sequence of method calls and returns the result of each call in order.
Each operation is one of:
- `('deposit', accountId, amount)`
- `('withdraw', accountId, amount)`
- `('transfer', fromAccountId, toAccountId, amount)`
- `('getBalance', accountId)`
Rules:
- `amount` is always a positive integer.
- If an account does not exist yet, its balance should be treated as `0`.
- `withdraw` succeeds only if the account has enough money.
- `transfer` must be atomic: either money is moved from one account to the other, or no balance changes at all.
- Return one result per operation:
- `deposit` returns the new balance of that account.
- `withdraw` returns `True` if it succeeds, otherwise `False`.
- `transfer` returns `True` if it succeeds, otherwise `False`.
- `getBalance` returns the current balance.
Note: Real interview follow-up discussion may ask how to make this thread-safe and deadlock-free. For this coding task, process the operations sequentially while preserving correct account behavior and atomic transfers.
Constraints
- 0 <= len(operations) <= 200000
- 1 <= amount <= 10^9 for deposit, withdraw, and transfer operations
- Account IDs are strings
- All operation names are valid and all amounts are positive integers