Stripe Coding Interview: Match Payments to Invoices

Overview

You are given two collections — invoices and payments — and must implement a deterministic, one-to-one matching procedure that assigns at most one invoice to each payment. For every payment (preserve input order) you should attempt prioritized strategies: identifier match (invoice_id or account_id), exact amount match, then a configurable range/forgiveness match. Once an invoice is assigned it cannot be reused.

What you'll be asked to do

You should return, for each payment, the payment_id, the matched_invoice_id (or null), and the signed numeric difference payment_amount - invoice_amount (or null if unmatched). If multiple invoices satisfy a strategy, pick the invoice with the earliest due date; if due dates tie, apply a deterministic tie-breaker (e.g., lexical invoice_id). Exact equality takes precedence over range matches.

Flow or stages to implement

1. Process payments in input order.
2. For each payment, apply strategies in priority order and stop at the first that yields candidates.
3. Filter out invoices already assigned, sort candidates by due date and tie-breaker, pick the first.
4. Compute signed difference and mark invoice used.

Skill signals interviewers look for

You should demonstrate careful handling of dates and numeric comparisons (currency/tolerance), deterministic ordering and tie-breakers, efficient lookups (hash maps / indexing), and stable, reproducible behavior. Be ready to discuss edge cases (duplicate identifiers, floating-point tolerance, time zones, and performance at scale).