Design Splitwise

Difficulty: Hard Source: awesome-low-level-design

Requirements

  1. Create accounts, manage profiles
  2. Create groups, add users
  3. Add expenses with amount, description, participants
  4. Auto-split expenses by share
  5. View balances, settle up
  6. Different split methods: equal, percentage, exact
  7. View transaction history
  8. Handle concurrent transactions

Class Diagram

Class Diagram

Classes, Interfaces and Enumerations

Class/Interface Description
User Id, name, email, balance map with other users
Group Member list, expense list
Expense Id, amount, description, paying user, splits list
Split Abstract class; EqualSplit, PercentSplit, ExactSplit subclasses
EqualSplit Splits expense equally among all participants
PercentSplit Splits expense by percentage for each participant
ExactSplit Splits expense by exact amounts for each participant
Transaction Id, sender, receiver, amount
SplitwiseService Singleton; ConcurrentHashMap + CopyOnWriteArrayList

Design Patterns Used

Pattern Application
Singleton SplitwiseService provides centralized management of users, groups, and expenses
Inheritance/Polymorphism Split hierarchy allows flexible expense splitting strategies (equal, percentage, exact) through a common abstract interface

Code Implementations

Language Source Code
Java View on GitHub
Python View on GitHub
C++ View on GitHub
C# View on GitHub
Go View on GitHub