Zig: completed Knapsack

zig/knapsack/.exercism/config.json

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+{
+  "authors": [
+    "keiravillekode"
+  ],
+  "files": {
+    "solution": [
+      "knapsack.zig"
+    ],
+    "test": [
+      "test_knapsack.zig"
+    ],
+    "example": [
+      ".meta/example.zig"
+    ]
+  },
+  "blurb": "Given a knapsack that can only carry a certain weight, determine which items to put in the knapsack in order to maximize their combined value.",
+  "source": "Wikipedia",
+  "source_url": "https://en.wikipedia.org/wiki/Knapsack_problem"
+}

zig/knapsack/.exercism/metadata.json

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+{"track":"zig","exercise":"knapsack","id":"958dbce812a24b8b8163738aa9831568","url":"https://exercism.org/tracks/zig/exercises/knapsack","handle":"Chomp1295","is_requester":true,"auto_approve":false}

zig/knapsack/HELP.md

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+# Help
+
+## Running the tests
+
+Write your code in `<exercise_name>.zig`.
+
+To run the tests for an exercise, run:
+
+```bash
+zig test test_exercise_name.zig
+```
+
+in the exercise's root directory (replacing `exercise_name` with the name of the exercise).
+
+## Submitting your solution
+
+You can submit your solution using the `exercism submit knapsack.zig` command.
+This command will upload your solution to the Exercism website and print the solution page's URL.
+
+It's possible to submit an incomplete solution which allows you to:
+
+- See how others have completed the exercise
+- Request help from a mentor
+
+## Need to get help?
+
+If you'd like help solving the exercise, check the following pages:
+
+- The [Zig track's documentation](https://exercism.org/docs/tracks/zig)
+- The [Zig track's programming category on the forum](https://forum.exercism.org/c/programming/zig)
+- [Exercism's programming category on the forum](https://forum.exercism.org/c/programming/5)
+- The [Frequently Asked Questions](https://exercism.org/docs/using/faqs)
+
+Should those resources not suffice, you could submit your (incomplete) solution to request mentoring.
+
+- [The Zig Programming Language Documentation][documentation] is a great overview of all of the language features that Zig provides to those who use it.
+- [Zig Guide][zig-guide] is an excellent primer that explains the language features that Zig has to offer.
+- [Ziglings][ziglings] is highly recommended.
+  Learn Zig by fixing tiny broken programs.
+- [The Zig Programming Language Discord][discord-zig] is the main [Discord][discord].
+  It provides a great way to get in touch with the Zig community at large, and get some quick, direct help for any Zig related problem.
+- [#zig][irc] on irc.freenode.net is the main Zig IRC channel.
+- [/r/Zig][reddit] is the main Zig subreddit.
+- [Stack Overflow][stack-overflow] can be used to discover code snippets and solutions to problems that may have already asked and maybe solved by others.
+
+[discord]: https://discordapp.com
+[discord-zig]: https://discord.com/invite/gxsFFjE
+[documentation]: https://ziglang.org/documentation/master
+[irc]: https://webchat.freenode.net/?channels=%23zig
+[reddit]: https://www.reddit.com/r/Zig
+[stack-overflow]: https://stackoverflow.com/questions/tagged/zig
+[zig-guide]: https://zig.guide/
+[ziglings]: https://codeberg.org/ziglings/exercises

zig/knapsack/README.md

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+# Knapsack
+
+Welcome to Knapsack on Exercism's Zig Track.
+If you need help running the tests or submitting your code, check out `HELP.md`.
+
+## Introduction
+
+Bob is a thief.
+After months of careful planning, he finally manages to crack the security systems of a fancy store.
+
+In front of him are many items, each with a value and weight.
+Bob would gladly take all of the items, but his knapsack can only hold so much weight.
+Bob has to carefully consider which items to take so that the total value of his selection is maximized.
+
+## Instructions
+
+Your task is to determine which items to take so that the total value of his selection is maximized, taking into account the knapsack's carrying capacity.
+
+Items will be represented as a list of items.
+Each item will have a weight and value.
+All values given will be strictly positive.
+Bob can take only one of each item.
+
+For example:
+
+```text
+Items: [
+  { "weight": 5, "value": 10 },
+  { "weight": 4, "value": 40 },
+  { "weight": 6, "value": 30 },
+  { "weight": 4, "value": 50 }
+]
+
+Knapsack Maximum Weight: 10
+```
+
+For the above, the first item has weight 5 and value 10, the second item has weight 4 and value 40, and so on.
+In this example, Bob should take the second and fourth item to maximize his value, which, in this case, is 90.
+He cannot get more than 90 as his knapsack has a weight limit of 10.
+
+## Source
+
+### Created by
+
+- @keiravillekode
+
+### Based on
+
+Wikipedia - https://en.wikipedia.org/wiki/Knapsack_problem

zig/knapsack/knapsack.zig

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+const std = @import("std");
+const mem = std.mem;
+
+pub const Item = struct {
+    weight: usize,
+    value: usize,
+
+    pub fn init(weight: usize, value: usize) Item {
+        return Item{ .weight = weight, .value = value };
+    }
+};
+
+pub fn maximumValue(allocator: mem.Allocator, maximumWeight: usize, items: []const Item) !usize {
+    if (items.len == 0) return 0;
+
+    var dp: []usize = try allocator.alloc(usize, maximumWeight + 1);
+    defer allocator.free(dp);
+    @memset(dp, 0);
+
+    for (items) |item| {
+        var maxW = maximumWeight;
+        while (maxW > 0) : (maxW -= 1) {
+            if (item.weight <= maxW) {
+                dp[maxW] = @max(dp[maxW], dp[maxW - item.weight] + item.value);
+            }
+        }
+    }
+
+    return dp[maximumWeight];
+}

zig/knapsack/test_knapsack.zig

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+const std = @import("std");
+const testing = std.testing;
+
+const knapsack = @import("knapsack.zig");
+const Item = knapsack.Item;
+
+test "no items" {
+    const expected: usize = 0;
+    const items: [0]Item = .{};
+    const actual = try knapsack.maximumValue(testing.allocator, 100, &items);
+    try testing.expectEqual(expected, actual);
+}
+
+test "one item, too heavy" {
+    const expected: usize = 0;
+    const items: [1]Item = .{
+        Item.init(100, 1),
+    };
+    const actual = try knapsack.maximumValue(testing.allocator, 10, &items);
+    try testing.expectEqual(expected, actual);
+}
+
+test "five items (cannot be greedy by weight)" {
+    const expected: usize = 21;
+    const items: [5]Item = .{
+        Item.init(2, 5),
+        Item.init(2, 5),
+        Item.init(2, 5),
+        Item.init(2, 5),
+        Item.init(10, 21),
+    };
+    const actual = try knapsack.maximumValue(testing.allocator, 10, &items);
+    try testing.expectEqual(expected, actual);
+}
+
+test "five items (cannot be greedy by value)" {
+    const expected: usize = 80;
+    const items: [5]Item = .{
+        Item.init(2, 20),
+        Item.init(2, 20),
+        Item.init(2, 20),
+        Item.init(2, 20),
+        Item.init(10, 50),
+    };
+    const actual = try knapsack.maximumValue(testing.allocator, 10, &items);
+    try testing.expectEqual(expected, actual);
+}
+
+test "example knapsack" {
+    const expected: usize = 90;
+    const items: [4]Item = .{
+        Item.init(5, 10),
+        Item.init(4, 40),
+        Item.init(6, 30),
+        Item.init(4, 50),
+    };
+    const actual = try knapsack.maximumValue(testing.allocator, 10, &items);
+    try testing.expectEqual(expected, actual);
+}
+
+test "8 items" {
+    const expected: usize = 900;
+    const items: [8]Item = .{
+        Item.init(25, 350),
+        Item.init(35, 400),
+        Item.init(45, 450),
+        Item.init(5, 20),
+        Item.init(25, 70),
+        Item.init(3, 8),
+        Item.init(2, 5),
+        Item.init(2, 5),
+    };
+    const actual = try knapsack.maximumValue(testing.allocator, 104, &items);
+    try testing.expectEqual(expected, actual);
+}
+
+test "15 items" {
+    const expected: usize = 1458;
+    const items: [15]Item = .{
+        Item.init(70, 135),
+        Item.init(73, 139),
+        Item.init(77, 149),
+        Item.init(80, 150),
+        Item.init(82, 156),
+        Item.init(87, 163),
+        Item.init(90, 173),
+        Item.init(94, 184),
+        Item.init(98, 192),
+        Item.init(106, 201),
+        Item.init(110, 210),
+        Item.init(113, 214),
+        Item.init(115, 221),
+        Item.init(118, 229),
+        Item.init(120, 240),
+    };
+    const actual = try knapsack.maximumValue(testing.allocator, 750, &items);
+    try testing.expectEqual(expected, actual);
+}