An extensibly/modularly/cleanly coded system design for SplitWise Functionalities: 1. User can split spend with another user - Based on percentage - Absolute values - Equally 2. User can split spend with a group 3. User can exclude few people from the group while adding expense 4. User can simplify debts - A owes money to B, B owes money to C. If B chooses to simplify debts, then A will pay to C directly Future plan: User should be able to export their monthly summary of expenses and dues The code is extensible, modular and clean. Choice of data structure was important for extensibility of the code. Took some time to think through it. Started working from the first requirement and modelled other requirements on top of it.