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Splitwise - Low Level Design

A low-level design implementation of a Splitwise-style expense sharing system built to explore scalable backend architecture, clean object-oriented design, and maintainable financial workflow modeling.

This project focuses on designing modular and extensible components commonly used in real-world expense management and payment settlement systems.

Problem Statement

Design a system that allows users to:

  • Create groups
  • Add shared expenses
  • Split expenses among users
  • Track balances between participants
  • Simplify and settle debts
  • Maintain transaction history

The system should be scalable, maintainable, and extensible for future enhancements.

Features

  • User management
  • Group expense tracking
  • Equal / exact / percentage expense splitting
  • Balance calculation
  • Debt settlement workflows
  • Transaction history management
  • Modular class structure
  • Extensible expense models

Design Goals

The system was designed with emphasis on:

  • scalability
  • maintainability
  • extensibility
  • separation of concerns
  • reusable architecture
  • clean object-oriented design

Concepts Explored

  • Low-Level Design (LLD)
  • Object-Oriented Programming (OOP)
  • SOLID Principles
  • Financial workflow modeling
  • Transaction lifecycle handling
  • Service abstraction
  • Domain-driven design thinking

Core Entities

  • User
  • Group
  • Expense
  • Split
  • Balance Sheet
  • Transaction
  • Settlement Manager

Expense Split Types

Equal Split

Expense divided equally among participants.

Exact Split

Custom exact amount assigned to each participant.

Percentage Split

Expense divided based on percentage contribution.

Possible Real-World Extensions

  • Payment gateway integration
  • Multi-currency support
  • Notification systems
  • Expense categories & analytics
  • Recurring expenses
  • Fraud detection workflows
  • Async settlement processing
  • Distributed transaction handling

Tech Stack

  • C++
  • Object-Oriented Programming
  • Low-Level Design
  • Design Patterns

Repository Structure

Splitwise-LLD/
├── models/
├── services/
├── managers/
├── main.cpp
└── README.md