Add food-chain exercise (#438)

config.json

@@ -90,6 +90,14 @@
         "prerequisites": [],
         "difficulty": 2
       },
+      {
+        "slug": "food-chain",
+        "name": "Food Chain",
+        "uuid": "fe7bad93-d829-4308-9eed-68ad6e5d522f",
+        "practices": [],
+        "prerequisites": [],
+        "difficulty": 5
+      },
       {
         "slug": "collatz-conjecture",
         "name": "Collatz Conjecture",

exercises/practice/food-chain/.docs/instructions.md

@@ -0,0 +1,64 @@
+# Instructions
+
+Generate the lyrics of the song 'I Know an Old Lady Who Swallowed a Fly'.
+
+While you could copy/paste the lyrics, or read them from a file, this problem is much more interesting if you approach it algorithmically.
+
+This is a [cumulative song][cumulative-song] of unknown origin.
+
+This is one of many common variants.
+
+```text
+I know an old lady who swallowed a fly.
+I don't know why she swallowed the fly. Perhaps she'll die.
+
+I know an old lady who swallowed a spider.
+It wriggled and jiggled and tickled inside her.
+She swallowed the spider to catch the fly.
+I don't know why she swallowed the fly. Perhaps she'll die.
+
+I know an old lady who swallowed a bird.
+How absurd to swallow a bird!
+She swallowed the bird to catch the spider that wriggled and jiggled and tickled inside her.
+She swallowed the spider to catch the fly.
+I don't know why she swallowed the fly. Perhaps she'll die.
+
+I know an old lady who swallowed a cat.
+Imagine that, to swallow a cat!
+She swallowed the cat to catch the bird.
+She swallowed the bird to catch the spider that wriggled and jiggled and tickled inside her.
+She swallowed the spider to catch the fly.
+I don't know why she swallowed the fly. Perhaps she'll die.
+
+I know an old lady who swallowed a dog.
+What a hog, to swallow a dog!
+She swallowed the dog to catch the cat.
+She swallowed the cat to catch the bird.
+She swallowed the bird to catch the spider that wriggled and jiggled and tickled inside her.
+She swallowed the spider to catch the fly.
+I don't know why she swallowed the fly. Perhaps she'll die.
+
+I know an old lady who swallowed a goat.
+Just opened her throat and swallowed a goat!
+She swallowed the goat to catch the dog.
+She swallowed the dog to catch the cat.
+She swallowed the cat to catch the bird.
+She swallowed the bird to catch the spider that wriggled and jiggled and tickled inside her.
+She swallowed the spider to catch the fly.
+I don't know why she swallowed the fly. Perhaps she'll die.
+
+I know an old lady who swallowed a cow.
+I don't know how she swallowed a cow!
+She swallowed the cow to catch the goat.
+She swallowed the goat to catch the dog.
+She swallowed the dog to catch the cat.
+She swallowed the cat to catch the bird.
+She swallowed the bird to catch the spider that wriggled and jiggled and tickled inside her.
+She swallowed the spider to catch the fly.
+I don't know why she swallowed the fly. Perhaps she'll die.
+
+I know an old lady who swallowed a horse.
+She's dead, of course!
+```
+
+[cumulative-song]: https://en.wikipedia.org/wiki/Cumulative_song

exercises/practice/food-chain/.meta/config.json

@@ -0,0 +1,19 @@
+{
+  "authors": [
+    "keiravillekode"
+  ],
+  "files": {
+    "solution": [
+      "food_chain.zig"
+    ],
+    "test": [
+      "test_food_chain.zig"
+    ],
+    "example": [
+      ".meta/example.zig"
+    ]
+  },
+  "blurb": "Generate the lyrics of the song 'I Know an Old Lady Who Swallowed a Fly'.",
+  "source": "Wikipedia",
+  "source_url": "https://en.wikipedia.org/wiki/There_Was_an_Old_Lady_Who_Swallowed_a_Fly"
+}

exercises/practice/food-chain/.meta/example.zig

@@ -0,0 +1,76 @@
+const std = @import("std");
+
+const i_know = "I know an old lady who swallowed a ";
+
+const stop = ".\n";
+
+const she_swallowed = "She swallowed the ";
+
+const to_catch = " to catch the ";
+
+const that_wriggled = " that wriggled and jiggled and tickled inside her";
+
+const animals = [_][]const u8{ "", "fly", "spider", "bird", "cat", "dog", "goat", "cow", "horse" };
+
+const exclamations = [_][]const u8{
+    "",
+    "I don't know why she swallowed the fly. Perhaps she'll die.",
+    "It wriggled and jiggled and tickled inside her.\n",
+    "How absurd to swallow a bird!\n",
+    "Imagine that, to swallow a cat!\n",
+    "What a hog, to swallow a dog!\n",
+    "Just opened her throat and swallowed a goat!\n",
+    "I don't know how she swallowed a cow!\n",
+    "She's dead, of course!"
+};
+
+fn appendString(buffer: []u8, offset: *usize, str: []const u8) void {
+    @memcpy(buffer[offset.*..(offset.* + str.len)], str);
+    offset.* += str.len;
+}
+
+pub fn recite(buffer: []u8, start_verse: u32, end_verse: u32) []const u8 {
+    var offset: usize = 0;
+
+    for (start_verse..end_verse+1) |verse| {
+        if (verse != start_verse) {
+            buffer[offset] = '\n';
+            buffer[offset + 1] = '\n';
+            offset += 2;
+        }
+
+        appendString(buffer, &offset, i_know);
+
+        appendString(buffer, &offset, animals[verse]);
+
+        appendString(buffer, &offset, stop);
+
+        appendString(buffer, &offset, exclamations[verse]);
+
+        if (verse == 1 or verse == 8) {
+            continue;
+        }
+
+        var animal = verse;
+        while (animal > 1) {
+            appendString(buffer, &offset, she_swallowed);
+
+            appendString(buffer, &offset, animals[animal]);
+
+            appendString(buffer, &offset, to_catch);
+
+            animal -= 1;
+            appendString(buffer, &offset, animals[animal]);
+
+            if (animal == 2) {
+                appendString(buffer, &offset, that_wriggled);
+            }
+
+            appendString(buffer, &offset, stop);
+        }
+
+        appendString(buffer, &offset, exclamations[1]);
+    }
+
+    return buffer[0..offset];
+}

exercises/practice/food-chain/.meta/tests.toml

@@ -0,0 +1,40 @@
+# 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.
+
+[751dce68-9412-496e-b6e8-855998c56166]
+description = "fly"
+
+[6c56f861-0c5e-4907-9a9d-b2efae389379]
+description = "spider"
+
+[3edf5f33-bef1-4e39-ae67-ca5eb79203fa]
+description = "bird"
+
+[e866a758-e1ff-400e-9f35-f27f28cc288f]
+description = "cat"
+
+[3f02c30e-496b-4b2a-8491-bc7e2953cafb]
+description = "dog"
+
+[4b3fd221-01ea-46e0-825b-5734634fbc59]
+description = "goat"
+
+[1b707da9-7001-4fac-941f-22ad9c7a65d4]
+description = "cow"
+
+[3cb10d46-ae4e-4d2c-9296-83c9ffc04cdc]
+description = "horse"
+
+[22b863d5-17e4-4d1e-93e4-617329a5c050]
+description = "multiple verses"
+
+[e626b32b-745c-4101-bcbd-3b13456893db]
+description = "full song"

exercises/practice/food-chain/food_chain.zig

@@ -0,0 +1,6 @@
+pub fn recite(buffer: []u8, start_verse: u32, end_verse: u32) []const u8 {
+    _ = buffer;
+    _ = start_verse;
+    _ = end_verse;
+    @compileError("please implement the recite function");
+}