Supermarket Checkout

algorithm

Medium

pricing

discounts

dictionary

kata

Supermarket Checkout

Your retail customer's self-checkout needs a pricing brain: a plain price list, weekly multibuy offers ("3 for the price of 2"), and bulk breaks that reprice the whole line once a minimum quantity is reached — the same trio Business Central models with sales prices and line discounts, distilled into a kata.

Items are scanned one at a time, in whatever order the shopper unloads the basket, and the display shows a running total after every beep.

Requirements

Create a codeunit named "Checkout Pricing" with five public procedures:

procedure SetUnitPrice(ItemCode: Code[20]; UnitPrice: Decimal)
procedure SetMultibuyOffer(ItemCode: Code[20]; OfferQuantity: Integer; OfferPrice: Decimal)
procedure SetBulkPrice(ItemCode: Code[20]; MinimumQuantity: Integer; DiscountedUnitPrice: Decimal)
procedure Scan(ItemCode: Code[20])
procedure Total(): Decimal

Each grading test configures prices and deals, scans items, and reads Total() through one "Checkout Pricing" codeunit variable — whatever you keep inside the codeunit lives as long as that variable, and every test starts with a fresh one.

Pricing rules — all of them are graded:

An item with no deal costs its unit price times the scanned quantity.
A multibuy offer SetMultibuyOffer(Item, N, P) charges P for every complete group of N scanned units of that item; leftover units beyond the complete groups are charged at the unit price. A classic "3 for the price of 2" is simply N = 3 with P set to twice the unit price.
A bulk break SetBulkPrice(Item, M, D) reprices every unit — including the first — at D once the scanned quantity reaches M or more; below M, all units cost the normal unit price.
Scans of the same item count together no matter how they are interleaved with other items — MILK, BREAD, MILK, MILK holds three milks.
Total() may be called at any time and any number of times: it prices the basket scanned so far and must not disturb later scans or later totals.
An empty basket totals 0.
Scan of an item that has no configured unit price must raise an error with a message that contains the item's code and the text no price (lowercase).

What you may rely on — the tests never violate this:

The unit price of an item is always configured before any deal for it and before it is scanned.
Prices are positive with at most 2 decimal places; OfferQuantity and MinimumQuantity are at least 2.
An item carries at most one deal — never both a multibuy offer and a bulk break.
No rounding is involved: every expected total is an exact sum of the configured prices.

Worked example: BREAD at 1.15; MILK at 0.85 with a multibuy of 3 for 2.00; SUGAR at 2.00 with a bulk break from 5 units at 1.70. Scanning MILK, BREAD, MILK, MILK, MILK totals 4.00 — one complete milk group at 2.00, the fourth milk at 0.85, plus the bread. Scanning SUGAR five times totals 8.50 — not 9.70: the bulk price reaches back and reprices the first four units too.

What the tests check

The tests price a single scan and a plain multi-item basket; a complete multibuy group, a quantity below the offer, and a quantity spanning two groups plus a remainder; offer groups formed from interleaved scans; a bulk break one unit below its minimum and exactly at it; a running total read mid-basket and again after more scans; an empty basket; the no price error for an unknown item (checked via the expected error text); and one randomized basket combining all three deal shapes whose expected total the test computes independently — so neither hardcoding the examples nor pricing at scan time passes.

Learn More

Hint 1

Score the basket, not the beep: a deal can only be judged once you know an item's full scanned quantity, so keep a running tally per item and do all pricing when Total is asked. Interleaved scans and mid-basket totals then cost nothing extra.

Hint 2

Multibuy is integer division: with quantity Q on an offer of N for P, Q div N complete groups cost P each and the Q mod N leftovers cost the plain unit price. A bulk break is one comparison — once Q reaches the minimum, the discounted unit price replaces the normal one for every unit, including the first; below it, nothing changes.

Hint 3

Dictionaries keyed by item code carry the whole checkout: one for unit prices, a few for each deal's parameters, one for scanned quantities. Scan errors when the price dictionary has no entry for the item; otherwise it bumps the item's tally. Total walks the tally and prices each line by whichever deal the item carries — multibuy math, bulk comparison, or plain quantity times unit price.

ALBusiness Central 28.4

Press Compile to check your code compiles — Submit runs the tests.

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