Implement inventory allocation with backorders

Q: Implement inventory allocation with backorders

This is a Coding & Algorithms interview question from Amazon for Machine Learning Engineer roles. View the full question and solution on PracHub.

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Question

Design and implement a function to process an event stream for an e-commerce marketplace. Input: (

initial inventory as a list of (sku: string, qty: int); (
events ordered by timestamp, each either Order(orderId: string, items: [(sku, qty)]) or Restock(items: [(sku, qty)]). Rules: For each Order, allocate from current inventory by SKU; if insufficient, fulfill what you can and record the remainder as a backorder for that order. When a Restock arrives, allocate to outstanding backorders in FIFO order before increasing on-hand inventory. Output: after all events, return (a) per-order fulfillment details (fulfilled and backordered quantities per SKU and whether fully fulfilled) and (b) final on-hand inventory by SKU. Constraints: up to 1e5 events and 1e5 distinct SKUs; target time O(E log S) and space O(S + B). Describe the data structures you would use (e.g., hash maps, heaps, queues) and analyze complexity. How would you extend this to support order cancellation in O(log S)?

Implement inventory allocation with backorders

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