Practice/Anthropic/Banking System (Online Assessment)

Banking System (Online Assessment)

CodingMust

Problem Overview

You are implementing an in-memory banking system with four progressive levels of complexity. Each level builds on the previous one, adding new features and operations.

This is a typical online assessment (OA) problem where levels are unlocked sequentially. Plan your design carefully to accommodate future requirements.

Level Summary

• Level 1: Basic account operations (create, deposit, transfer)
• Level 2: Ranking accounts by spending activity
• Level 3: Scheduled payments with cashback and status tracking
• Level 4: Account merging and historical balance queries

Important Notes

• Timestamps are in milliseconds and strictly increasing
• Design data structures that can be extended for future levels
• Test your code thoroughly before moving to the next level

Level 1: Basic Account Operations

Initially, the banking system contains no accounts. Implement operations for account creation, deposits, and transfers.

Operations

create_account(timestamp, account_id)

• Creates a new account with the given identifier
• Returns True if successful, False if account already exists

deposit(timestamp, account_id, amount)

• Deposits money into the specified account
• Returns the balance after deposit
• Returns None if account doesn't exist

transfer(timestamp, source_account_id, target_account_id, amount)

• Transfers money from source to target account

• Returns source account balance after transfer

• Returns None if:

  • Either account doesn't exist
  • Source and target are the same
  • Source has insufficient funds

Example

bank = BankingSystem() bank.create_account(1, "acc1") # True bank.deposit(2, "acc1", 100) # 100 bank.create_account(3, "acc2") # True bank.transfer(4, "acc1", "acc2", 30) # 70 (acc1 balance)

Requirements

• Maintain account balances
• Validate operations (account existence, sufficient funds)
• Process operations in timestamp order

Level 2: Top Spenders

The bank wants to identify accounts with high outgoing transactions. Implement ranking by total spending.

New Operation

top_spenders(timestamp, n)

• Returns top n accounts by total outgoing transactions
• Outgoing transactions include transfers and payments (from Level 3)
• Sort by total outgoing amount (descending), then alphabetically by account_id
• Format: ["account_id_1(total_1)", "account_id_2(total_2)", ...]

Example

` bank.top_spenders(100, 3)

Returns: ["acc1(500)", "acc3(450)", "acc2(200)"]

`

Requirements

• Track total outgoing amount for each account
• Efficient sorting and ranking
• Handle ties with alphabetical ordering
• Cashback (Level 3) should NOT count as outgoing

Level 3: Scheduled Payments with Cashback

Support withdrawals with cashback rewards that are credited after a delay.

New Operations

pay(timestamp, account_id, amount)

• Withdraws amount from account
• Provides 2% cashback (rounded down)
• Cashback credited after 24 hours (86400000 ms)
• Returns unique payment ID (e.g., "payment1", "payment2")
• Returns None if account doesn't exist or has insufficient funds

get_payment_status(timestamp, account_id, payment)

• Returns payment status for given payment ID
• Returns "IN_PROGRESS" if cashback not yet received
• Returns "CASHBACK_RECEIVED" if cashback has been credited
• Returns None if invalid account/payment

Example

` payment_id = bank.pay(1000, "acc1", 100)

Withdraws 100, schedules 2 cashback at timestamp 87400000

status = bank.get_payment_status(5000, "acc1", payment_id)

Returns: "IN_PROGRESS"

status = bank.get_payment_status(90000000, "acc1", payment_id)

Returns: "CASHBACK_RECEIVED"

`

Requirements

• Calculate cashback: int(amount * 0.02)
• Schedule cashback at timestamp + 86400000
• Track payment status
• Update top_spenders to include pay operations

Level 4: Account Merging and Historical Balances

Support merging accounts while preserving history, and querying past balances.

New Operations

merge_accounts(timestamp, account_id_1, account_id_2)

• Merges account_id_2 into account_id_1
• Combines balances, histories, and pending cashbacks
• Removes account_id_2 after merge
• Returns True if successful, False if invalid

get_balance(timestamp, account_id, time_at)

• Returns account balance at timestamp time_at
• Returns None if account didn't exist at that time
• Must reflect merged account history

Merge Behavior

• Balance of account_id_2 added to account_id_1
• Pending cashbacks for account_id_2 redirected to account_id_1
• Payment statuses transferred (check with account_id_1)
• Outgoing totals combined for top_spenders
• account_id_2 can be recreated after merge (starts fresh)

Example

` bank.merge_accounts(1000, "acc1", "acc2")

acc1 now has combined balance and history

balance = bank.get_balance(2000, "acc1", 500)

Returns balance at timestamp 500 (before merge)

`

Important Edge Cases

• Historical queries after merge: queries with time_at < merge_time return pre-merge balance
• Account recreation: after merge, account_id_2 can be created again with fresh state
• Merged account inherits all history and pending operations