Design an expense-splitting app

Medium40 minFree, no account

Money that must balance to the cent, and a settlement graph worth simplifying.

The question

Design the core of Splitwise: people in a group record expenses, split them in several ways, and settle up.

Show who owes whom, minimising the number of payments.

Functional

Record an expense: payer, amount, participants, split type (equal, exact, percentage, shares).
Show each person's net balance in a group.
Suggest a minimal set of payments to settle.
Record a settlement payment.

Non-functional

Balances must sum to exactly zero. No cent may be created or lost.
History is immutable: an edit is a correcting entry, not an overwrite.

40:00Commit to an answer before you open the solution. Reading it first teaches you to recognise good answers, which is not the skill being tested.

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The worked solution

written by a person · not a grade

Score yourself

0 of 5 marked

Integer money with a deterministic remainder rule25
Split strategies behind an interface with the sum invariant20
Net balances derived from an immutable log rather than pairwise debts25
A settlement algorithm with an honest bound20
Edits modelled as corrections10

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