Sync book-store (#850)

Author: tomasnorre

exercises/practice/book-store/.docs/instructions.md

@@ -1,27 +1,20 @@
 # Instructions
 
-To try and encourage more sales of different books from a popular 5 book
-series, a bookshop has decided to offer discounts on multiple book purchases.
+To try and encourage more sales of different books from a popular 5 book series, a bookshop has decided to offer discounts on multiple book purchases.
 
 One copy of any of the five books costs $8.
 
-If, however, you buy two different books, you get a 5%
-discount on those two books.
+If, however, you buy two different books, you get a 5% discount on those two books.
 
 If you buy 3 different books, you get a 10% discount.
 
 If you buy 4 different books, you get a 20% discount.
 
 If you buy all 5, you get a 25% discount.
 
-Note: that if you buy four books, of which 3 are
-different titles, you get a 10% discount on the 3 that
-form part of a set, but the fourth book still costs $8.
+Note that if you buy four books, of which 3 are different titles, you get a 10% discount on the 3 that form part of a set, but the fourth book still costs $8.
 
-Your mission is to write a piece of code to calculate the
-price of any conceivable shopping basket (containing only
-books of the same series), giving as big a discount as
-possible.
+Your mission is to write code to calculate the price of any conceivable shopping basket (containing only books of the same series), giving as big a discount as possible.
 
 For example, how much does this basket of books cost?
 
@@ -33,36 +26,36 @@ For example, how much does this basket of books cost?
 
 One way of grouping these 8 books is:
 
-- 1 group of 5 --> 25% discount (1st,2nd,3rd,4th,5th)
-- +1 group of 3 --> 10% discount (1st,2nd,3rd)
+- 1 group of 5 (1st, 2nd,3rd, 4th, 5th)
+- 1 group of 3 (1st, 2nd, 3rd)
 
 This would give a total of:
 
 - 5 books at a 25% discount
-- +3 books at a 10% discount
+- 3 books at a 10% discount
 
 Resulting in:
 
-- 5 x (8 - 2.00) == 5 x 6.00 == $30.00
-- +3 x (8 - 0.80) == 3 x 7.20 == $21.60
+- 5 × (100% - 25%) × $8 = 5 × $6.00 = $30.00, plus
+- 3 × (100% - 10%) × $8 = 3 × $7.20 = $21.60
 
-For a total of $51.60
+Which equals $51.60.
 
 However, a different way to group these 8 books is:
 
-- 1 group of 4 books --> 20% discount  (1st,2nd,3rd,4th)
-- +1 group of 4 books --> 20% discount  (1st,2nd,3rd,5th)
+- 1 group of 4 books (1st, 2nd, 3rd, 4th)
+- 1 group of 4 books (1st, 2nd, 3rd, 5th)
 
 This would give a total of:
 
 - 4 books at a 20% discount
-- +4 books at a 20% discount
+- 4 books at a 20% discount
 
 Resulting in:
 
-- 4 x (8 - 1.60) == 4 x 6.40 == $25.60
-- +4 x (8 - 1.60) == 4 x 6.40 == $25.60
+- 4 × (100% - 20%) × $8 = 4 × $6.40 = $25.60, plus
+- 4 × (100% - 20%) × $8 = 4 × $6.40 = $25.60
 
-For a total of $51.20
+Which equals $51.20.
 
 And $51.20 is the price with the biggest discount.

exercises/practice/book-store/.meta/example.php

@@ -1,62 +1,42 @@
 <?php
 
-/*
- * By adding type hints and enabling strict type checking, code can become
- * easier to read, self-documenting and reduce the number of potential bugs.
- * By default, type declarations are non-strict, which means they will attempt
- * to change the original type to match the type specified by the
- * type-declaration.
- *
- * In other words, if you pass a string to a function requiring a float,
- * it will attempt to convert the string value to a float.
- *
- * To enable strict mode, a single declare directive must be placed at the top
- * of the file.
- * This means that the strictness of typing is configured on a per-file basis.
- * This directive not only affects the type declarations of parameters, but also
- * a function's return type.
- *
- * For more info review the Concept on strict type checking in the PHP track
- * <link>.
- *
- * To disable strict typing, comment out the directive below.
- */
-
-declare(strict_types=1);
-
-function total($items)
+function total(array $items): int
 {
-    return calculate($items, 0);
-}
+    $groups = array_fill(1, 5, 0); // Groups of books
+    $sets = array_fill(1, 5, 0);   // Sets by size
 
-function calculate($items, $total)
-{
-    if (empty($items)) {
-        return $total;
+    // Group the basket
+    foreach ($items as $bookId) {
+        $groups[$bookId]++;
     }
 
-    $group = array_unique($items);
-    $totalMin = INF;
-
-    for ($i = count($group); $i > 0; $i--) {
-        $itemsToRemove = array_flip(array_slice($group, 0, $i));
-        $itemsRemaining = array_filter($items, function ($x) use (&$itemsToRemove) {
-            if (array_key_exists($x, $itemsToRemove)) {
-                unset($itemsToRemove[$x]);
-                return false;
+    // Arrange groups into counts by set size
+    while (array_sum($groups) > 0) {
+        $setSize = 0;
+        foreach ($groups as $key => $count) {
+            if ($count > 0) {
+                $setSize++;
+                $groups[$key]--;
             }
-            return true;
-        });
-        $totalCurrent = calculate($itemsRemaining, $total + totalForGroup($i));
-        $totalMin = min([$totalMin, $totalCurrent]);
+        }
+        if ($setSize > 0) {
+            $sets[$setSize]++;
+        }
     }
 
-    return $totalMin;
-}
+    // Replace each 3set+5set with two 4sets
+    while ($sets[3] > 0 && $sets[5] > 0) {
+        $sets[3]--;
+        $sets[5]--;
+        $sets[4] += 2;
+    }
 
-function totalForGroup($count)
-{
-    $discount = [0, 0, 0.05, 0.1, 0.2, 0.25];
-    $price = 8;
-    return $price * $count * (1 - $discount[$count]);
+    // Calculate the total cost
+    $cost = 800 * $sets[1] +
+        (800 * 2 * 0.95) * $sets[2] +
+        (800 * 3 * 0.9) * $sets[3] +
+        (800 * 4 * 0.8) * $sets[4] +
+        (800 * 5 * 0.75) * $sets[5];
+
+    return (int)$cost;
 }

exercises/practice/book-store/.meta/tests.toml

@@ -1,6 +1,13 @@
-# This is an auto-generated file. Regular comments will be removed when this
-# file is regenerated. Regenerating will not touch any manually added keys,
-# so comments can be added in a "comment" key.
+# This is an auto-generated file.
+#
+# Regenerating this file via `configlet sync` will:
+# - Recreate every `description` key/value pair
+# - Recreate every `reimplements` key/value pair, where they exist in problem-specifications
+# - Remove any `include = true` key/value pair (an omitted `include` key implies inclusion)
+# - Preserve any other key/value pair
+#
+# As user-added comments (using the # character) will be removed when this file
+# is regenerated, comments can be added via a `comment` key.
 
 [17146bd5-2e80-4557-ab4c-05632b6b0d01]
 description = "Only a single book"
@@ -33,16 +40,25 @@ description = "Two groups of four is cheaper than groups of five and three"
 description = "Group of four plus group of two is cheaper than two groups of three"
 
 [68ea9b78-10ad-420e-a766-836a501d3633]
-description = "Two each of first 4 books and 1 copy each of rest"
+description = "Two each of first four books and one copy each of rest"
 
 [c0a779d5-a40c-47ae-9828-a340e936b866]
 description = "Two copies of each book"
 
 [18fd86fe-08f1-4b68-969b-392b8af20513]
-description = "Three copies of first book and 2 each of remaining"
+description = "Three copies of first book and two each of remaining"
 
 [0b19a24d-e4cf-4ec8-9db2-8899a41af0da]
-description = "Three each of first 2 books and 2 each of remaining books"
+description = "Three each of first two books and two each of remaining books"
 
 [bb376344-4fb2-49ab-ab85-e38d8354a58d]
 description = "Four groups of four are cheaper than two groups each of five and three"
+
+[5260ddde-2703-4915-b45a-e54dbbac4303]
+description = "Check that groups of four are created properly even when there are more groups of three than groups of five"
+
+[b0478278-c551-4747-b0fc-7e0be3158b1f]
+description = "One group of one and four is cheaper than one group of two and three"
+
+[cf868453-6484-4ae1-9dfc-f8ee85bbde01]
+description = "One group of one and two plus three groups of four is cheaper than one group of each size"

exercises/practice/book-store/BookStore.php

@@ -24,7 +24,10 @@
 
 declare(strict_types=1);
 
-function total(array $items): float
+/**
+ * Note: we expect the total in cents (1$ = 100 cents).
+ */
+function total(array $items): int
 {
     throw new \BadFunctionCallException("Implement the total function");
 }