Add book-store exercise (#442)

config.json

@@ -128,6 +128,14 @@
         ],
         "difficulty": 1
       },
+      {
+        "slug": "book-store",
+        "name": "Book Store",
+        "uuid": "cc192edb-a5d5-4f0d-a585-324641235cd5",
+        "practices": [],
+        "prerequisites": [],
+        "difficulty": 7
+      },
       {
         "slug": "pig-latin",
         "name": "Pig Latin",

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

@@ -0,0 +1,61 @@
+# 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.
+
+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 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.
+
+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?
+
+- 2 copies of the first book
+- 2 copies of the second book
+- 2 copies of the third book
+- 1 copy of the fourth book
+- 1 copy of the fifth book
+
+One way of grouping these 8 books is:
+
+- 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
+
+Resulting in:
+
+- 5 × (100% - 25%) × $8 = 5 × $6.00 = $30.00, plus
+- 3 × (100% - 10%) × $8 = 3 × $7.20 = $21.60
+
+Which equals $51.60.
+
+However, a different way to group these 8 books is:
+
+- 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
+
+Resulting in:
+
+- 4 × (100% - 20%) × $8 = 4 × $6.40 = $25.60, plus
+- 4 × (100% - 20%) × $8 = 4 × $6.40 = $25.60
+
+Which equals $51.20.
+
+And $51.20 is the price with the biggest discount.

exercises/practice/book-store/.meta/config.json

@@ -0,0 +1,19 @@
+{
+  "authors": [
+    "keiravillekode"
+  ],
+  "files": {
+    "solution": [
+      "book_store.zig"
+    ],
+    "test": [
+      "test_book_store.zig"
+    ],
+    "example": [
+      ".meta/example.zig"
+    ]
+  },
+  "blurb": "To try and encourage more sales of different books from a popular 5 book series, a bookshop has decided to offer discounts of multiple-book purchases.",
+  "source": "Inspired by the harry potter kata from Cyber-Dojo.",
+  "source_url": "https://cyber-dojo.org"
+}

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

@@ -0,0 +1,24 @@
+const std = @import("std");
+
+pub fn total(basket: []const u32) u32 {
+    var tally: [5]u32 = .{ 0, 0, 0, 0, 0 };
+    for (basket) |book| {
+        tally[book - 1] += 1;
+    }
+
+    std.mem.sort(u32, &tally, {}, comptime std.sort.desc(u32));
+
+    var five = tally[4];
+    var four = tally[3] - tally[4];
+    var three = tally[2] - tally[3];
+    const two = tally[1] - tally[2];
+    const one = tally[0] - tally[1];
+
+    // Two groups of four are cheaper than a group of five plus a group of three.
+    const adjustment = @min(three, five);
+    five -= adjustment;
+    three -= adjustment;
+    four += 2 * adjustment;
+
+    return 5 * five * 600 + 4 * four * 640 + 3 * three * 720 + 2 * two * 760 + 1 * one * 800;
+}

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

@@ -0,0 +1,64 @@
+# 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"
+
+[cc2de9ac-ff2a-4efd-b7c7-bfe0f43271ce]
+description = "Two of the same book"
+
+[5a86eac0-45d2-46aa-bbf0-266b94393a1a]
+description = "Empty basket"
+
+[158bd19a-3db4-4468-ae85-e0638a688990]
+description = "Two different books"
+
+[f3833f6b-9332-4a1f-ad98-6c3f8e30e163]
+description = "Three different books"
+
+[1951a1db-2fb6-4cd1-a69a-f691b6dd30a2]
+description = "Four different books"
+
+[d70f6682-3019-4c3f-aede-83c6a8c647a3]
+description = "Five different books"
+
+[78cacb57-911a-45f1-be52-2a5bd428c634]
+description = "Two groups of four is cheaper than group of five plus group of three"
+
+[f808b5a4-e01f-4c0d-881f-f7b90d9739da]
+description = "Two groups of four is cheaper than groups of five and three"
+
+[fe96401c-5268-4be2-9d9e-19b76478007c]
+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 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 two each of remaining"
+
+[0b19a24d-e4cf-4ec8-9db2-8899a41af0da]
+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/book_store.zig

@@ -0,0 +1,4 @@
+pub fn total(basket: []const u32) u32 {
+    _ = basket;
+    @compileError("please implement the total function");
+}

exercises/practice/book-store/test_book_store.zig

@@ -0,0 +1,94 @@
+const std = @import("std");
+const testing = std.testing;
+
+const book_store = @import("book_store.zig");
+
+test "Only a single book" {
+    const basket = &[_]u32{1};
+    try testing.expectEqual(800, book_store.total(basket));
+}
+
+test "Two of the same book" {
+    const basket = &[_]u32{ 2, 2 };
+    try testing.expectEqual(1600, book_store.total(basket));
+}
+
+test "Empty basket" {
+    const basket = &[_]u32{};
+    try testing.expectEqual(0, book_store.total(basket));
+}
+
+test "Two different books" {
+    const basket = &[_]u32{ 1, 2 };
+    try testing.expectEqual(1520, book_store.total(basket));
+}
+
+test "Three different books" {
+    const basket = &[_]u32{ 1, 2, 3 };
+    try testing.expectEqual(2160, book_store.total(basket));
+}
+
+test "Four different books" {
+    const basket = &[_]u32{ 1, 2, 3, 4 };
+    try testing.expectEqual(2560, book_store.total(basket));
+}
+
+test "Five different books" {
+    const basket = &[_]u32{ 1, 2, 3, 4, 5 };
+    try testing.expectEqual(3000, book_store.total(basket));
+}
+
+test "Two groups of four is cheaper than group of five plus group of three" {
+    const basket = &[_]u32{ 1, 1, 2, 2, 3, 3, 4, 5 };
+    try testing.expectEqual(5120, book_store.total(basket));
+}
+
+test "Two groups of four is cheaper than groups of five and three" {
+    const basket = &[_]u32{ 1, 1, 2, 3, 4, 4, 5, 5 };
+    try testing.expectEqual(5120, book_store.total(basket));
+}
+
+test "Group of four plus group of two is cheaper than two groups of three" {
+    const basket = &[_]u32{ 1, 1, 2, 2, 3, 4 };
+    try testing.expectEqual(4080, book_store.total(basket));
+}
+
+test "Two each of first four books and one copy each of rest" {
+    const basket = &[_]u32{ 1, 1, 2, 2, 3, 3, 4, 4, 5 };
+    try testing.expectEqual(5560, book_store.total(basket));
+}
+
+test "Two copies of each book" {
+    const basket = &[_]u32{ 1, 1, 2, 2, 3, 3, 4, 4, 5, 5 };
+    try testing.expectEqual(6000, book_store.total(basket));
+}
+
+test "Three copies of first book and two each of remaining" {
+    const basket = &[_]u32{ 1, 1, 2, 2, 3, 3, 4, 4, 5, 5, 1 };
+    try testing.expectEqual(6800, book_store.total(basket));
+}
+
+test "Three each of first two books and two each of remaining books" {
+    const basket = &[_]u32{ 1, 1, 2, 2, 3, 3, 4, 4, 5, 5, 1, 2 };
+    try testing.expectEqual(7520, book_store.total(basket));
+}
+
+test "Four groups of four are cheaper than two groups each of five and three" {
+    const basket = &[_]u32{ 1, 1, 2, 2, 3, 3, 4, 5, 1, 1, 2, 2, 3, 3, 4, 5 };
+    try testing.expectEqual(10240, book_store.total(basket));
+}
+
+test "Check that groups of four are created properly even when there are more groups of three than groups of five" {
+    const basket = &[_]u32{ 1, 1, 1, 1, 1, 1, 2, 2, 2, 2, 2, 2, 3, 3, 3, 3, 3, 3, 4, 4, 5, 5 };
+    try testing.expectEqual(14560, book_store.total(basket));
+}
+
+test "One group of one and four is cheaper than one group of two and three" {
+    const basket = &[_]u32{ 1, 1, 2, 3, 4 };
+    try testing.expectEqual(3360, book_store.total(basket));
+}
+
+test "One group of one and two plus three groups of four is cheaper than one group of each size" {
+    const basket = &[_]u32{ 1, 2, 2, 3, 3, 3, 4, 4, 4, 4, 5, 5, 5, 5, 5 };
+    try testing.expectEqual(10000, book_store.total(basket));
+}