Week 4: Lecture 3 — Coupons Are Algorithms
Thresholds, exclusions, stacking and bundles as rules with clear inputs — worked through live on three carts, one of them a trap.
17 August 2026
This lecture is the live version of Week 4: every discount rule is written down with clear inputs and conditions, instead of treated as a trick to guess. The deck adds two worked examples the week page only summarises — a threshold that costs more to satisfy than it saves, and a bundle that looks generous and isn’t — before handing the class a small cart to solve themselves.
Outline#
- why a coupon rule needs clear inputs: cart in, discount or refusal out
- thresholds, exclusions, stacking and bundles, one at a time
- worked example: a simple cart with one rule
- worked example: the threshold trap, where satisfying a minimum spend costs more than it saves
- worked example: a bundle that isn’t actually cheaper
- the $249 headphones with accessories, run through the same logic
- an in-class challenge cart, solved live
- how Assessment 2, Beat the Shopping Cart, reuses exactly this reasoning
Teaching team
- Idris Fenn — tutor