Stripe Mobile Engineer System Design Questions

Offline capabilities are essential for Stripe's mobile users, enabling transaction management without losing data when connectivity is limited. Design an Offline-First Sync Engine that ensures transactions are synchronized efficiently when online.
You should implement a class OfflineSyncEngine with methods to add, sync, and retrieve transactions.
- Method 1: addTransaction(Transaction tx) - adds a transaction locally.
- Method 2: syncTransactions() - syncs all locally added transactions to the server when online.
- Method 3: getTransactions() -> List<Transaction> - retrieves the list of transactions.Example 1:
Input: addTransaction(new Transaction(...))
Output: None
Input: syncTransactions()
Output: None
Input: getTransactions()
Output: List<Transaction>Constraints:
- The engine can handle up to 1000 transactions.

As part of Stripe’s financial services, representing fluctuating currency exchange rates in a tree structure can enable efficient querying and updates. This task involves creating an appropriate tree design to serve those needs.
You are to implement a class CurrencyExchangeTree with methods to add rates, remove rates, and retrieve the rate between two currencies efficiently.
- Method 1: addRate(String from, String to, double rate) - adds a new exchange rate.
- Method 2: removeRate(String from, String to) - removes an exchange rate.
- Method 3: getRate(String from, String to) -> double - Retrieves the exchange rate between two currencies.Example 1:
Input: addRate('USD', 'EUR', 0.84)
Output: None
Input: getRate('USD', 'EUR')
Output: 0.84Constraints:
- The tree can have at most 100 unique currency nodes.