Implement a Timestamped Banking System

Problem Statement

Design a system that tracks bank account balances over time. You need to support the following operations:

1. deposit(account_id, amount, timestamp): Adds amount to the account at the given timestamp. If a transaction already exists for this exact timestamp, update it.
2. get_balance(account_id, timestamp): Returns the balance of the account at the exact moment of the provided timestamp. If no transaction exists exactly at this timestamp, return the balance as it was after the most recent transaction prior to this timestamp (or 0 if none exist).
3. get_top_accounts(timestamp, k): Returns a list of the top k account_ids based on their balance at the given timestamp. If two accounts have the same balance, order by account_id ascending.

Constraints

• account_id: String (alphanumeric).
• amount: Integer.
• timestamp: Integer (non-negative).
• Total operations up to 10^5.
• k will be reasonable for output.

Examples

Example 1: deposit("A", 100, 1) deposit("B", 200, 2) get_balance("A", 5) -> returns 100 get_balance("A", 0) -> returns 0 get_top_accounts(3, 1) -> returns ["B"] (B has 200, A has 100)

Implementation

class BankSystem:
    def __init__(self):
        pass
    def deposit(self, account_id, amount, timestamp):
        pass
    def get_balance(self, account_id, timestamp):
        pass
    def get_top_accounts(self, timestamp, k):
        pass