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Pivot order-status counts

InstacartSoftware Engineer · Onsite
MediumSoftware EngineerOnsiteCoding & Algorithms

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This interview question evaluates algorithm design, data structures, correctness, complexity, edge cases, and implementation details in a realistic interview setting. A strong answer for Pivot order-status counts states assumptions, handles edge cases, explains trade-offs, and shows how to validate the result clearly.

Question

Given an orders table (order_id, shopper_id, order_date, status, …), pivot the data so that each row is one shopper and each column shows the count of orders for a specific status (e.g., DELIVERED, CANCELED, RETURNED). Provide an efficient Java solution that works on a platform without external date-parsing libraries.