Multithreaded Banking App Debug | Dataford Interview Questions

Given code for a banking application where multiple threads execute different functions in parallel, explain the code, identify bugs and suggest fixes/optimizations for multithreaded execution (e.g. locks, read-write lock, concurrent hash map). Asked in the Debugging round stage.

Implement the corrected transfer logic. Each transfer is [source, destination, amount]. Execute transfers in parallel, protect shared account balances, and avoid deadlocks. Inputs guarantee that every transfer is valid regardless of execution order.

Signature: def apply_transfers(balances, transfers):

Input: balances is a dictionary from account ID to integer balance. transfers is a list of transfer triples.

Output: Return a new dictionary containing final balances, without mutating the input dictionary.

Examples: {"A": 100, "B": 50}, [["A", "B", 30]] returns {"A": 70, "B": 80}. Two transfers involving the same account must still produce the correct combined balance.

Constraints

1 <= len(balances) <= 1000
0 <= balances[account] <= 10^9
0 <= len(transfers) <= 10^4
Each transfer has the form [source, destination, amount].
source and destination are distinct existing account IDs.
1 <= amount <= 10^9
Every transfer remains valid regardless of execution order.

Function Signature

def apply_transfers(balances, transfers):

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