Customer Checkout Duration

Problem Overview

• Process a stream of checkout events to determine and report when each customer leaves the store.
• Input: N instructions—CustomerEnter, BasketChange, LineService (per line or all lines); Output: exit notifications (customer IDs) in correct order, breaking ties by lower line ID.
• Context: supermarket lines; customers can’t switch lines, item increases send them to back, decreases keep position, zero items means immediate exit.
• From Optiver interviews; a coding interview problem and interview question.