Add dominoes exercise (#356)

Author: keiravillekode

config.json

@@ -891,6 +891,14 @@
         "prerequisites": [],
         "difficulty": 8
       },
+      {
+        "slug": "dominoes",
+        "name": "Dominoes",
+        "uuid": "93b688ab-47ae-4365-9f87-011e1ee174e1",
+        "practices": [],
+        "prerequisites": [],
+        "difficulty": 8
+      },
       {
         "slug": "zebra-puzzle",
         "name": "Zebra Puzzle",

exercises/practice/dominoes/.docs/instructions.md

@@ -0,0 +1,15 @@
+# Instructions
+
+Make a chain of dominoes.
+
+Compute a way to order a given set of domino stones so that they form a correct domino chain.
+In the chain, the dots on one half of a stone must match the dots on the neighboring half of an adjacent stone.
+Additionally, the dots on the halves of the stones without neighbors (the first and last stone) must match each other.
+
+For example given the stones `[2|1]`, `[2|3]` and `[1|3]` you should compute something
+like `[1|2] [2|3] [3|1]` or `[3|2] [2|1] [1|3]` or `[1|3] [3|2] [2|1]` etc, where the first and last numbers are the same.
+
+For stones `[1|2]`, `[4|1]` and `[2|3]` the resulting chain is not valid: `[4|1] [1|2] [2|3]`'s first and last numbers are not the same.
+4 != 3
+
+Some test cases may use duplicate stones in a chain solution, assume that multiple Domino sets are being used.

exercises/practice/dominoes/.docs/introduction.md

@@ -0,0 +1,13 @@
+# Introduction
+
+In Toyland, the trains are always busy delivering treasures across the city, from shiny marbles to rare building blocks.
+The tracks they run on are made of colorful domino-shaped pieces, each marked with two numbers.
+For the trains to move, the dominoes must form a perfect chain where the numbers match.
+
+Today, an urgent delivery of rare toys is on hold.
+You've been handed a set of track pieces to inspect.
+If they can form a continuous chain, the train will be on its way, bringing smiles across Toyland.
+If not, the set will be discarded, and another will be tried.
+
+The toys are counting on you to solve this puzzle.
+Will the dominoes connect the tracks and send the train rolling, or will the set be left behind?

exercises/practice/dominoes/.meta/config.json

@@ -0,0 +1,17 @@
+{
+  "authors": [
+    "keiravillekode"
+  ],
+  "files": {
+    "solution": [
+      "source/dominoes.d"
+    ],
+    "test": [
+      "source/dominoes.d"
+    ],
+    "example": [
+      "example/dominoes.d"
+    ]
+  },
+  "blurb": "Make a chain of dominoes."
+}

exercises/practice/dominoes/.meta/tests.toml

@@ -0,0 +1,49 @@
+# 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.
+
+[31a673f2-5e54-49fe-bd79-1c1dae476c9c]
+description = "empty input = empty output"
+
+[4f99b933-367b-404b-8c6d-36d5923ee476]
+description = "singleton input = singleton output"
+
+[91122d10-5ec7-47cb-b759-033756375869]
+description = "singleton that can't be chained"
+
+[be8bc26b-fd3d-440b-8e9f-d698a0623be3]
+description = "three elements"
+
+[99e615c6-c059-401c-9e87-ad7af11fea5c]
+description = "can reverse dominoes"
+
+[51f0c291-5d43-40c5-b316-0429069528c9]
+description = "can't be chained"
+
+[9a75e078-a025-4c23-8c3a-238553657f39]
+description = "disconnected - simple"
+
+[0da0c7fe-d492-445d-b9ef-1f111f07a301]
+description = "disconnected - double loop"
+
+[b6087ff0-f555-4ea0-a71c-f9d707c5994a]
+description = "disconnected - single isolated"
+
+[2174fbdc-8b48-4bac-9914-8090d06ef978]
+description = "need backtrack"
+
+[167bb480-dfd1-4318-a20d-4f90adb4a09f]
+description = "separate loops"
+
+[cd061538-6046-45a7-ace9-6708fe8f6504]
+description = "nine elements"
+
+[44704c7c-3adb-4d98-bd30-f45527cf8b49]
+description = "separate three-domino loops"

exercises/practice/dominoes/dub.sdl

@@ -0,0 +1,2 @@
+name "dominoes"
+buildRequirements "disallowDeprecations"

exercises/practice/dominoes/example/dominoes.d

@@ -0,0 +1,67 @@
+module dominoes;
+
+struct Stone {
+    int left;
+    int right;
+}
+
+pure bool canChain(immutable Stone[] dominoes)
+{
+    enum int n = 7; // values 0..6
+    int[n] parent;
+    int[n] rank;
+    int[n] tally;
+
+    foreach (i; 0 .. n)
+        parent[i] = i;
+
+    int find(int x)
+    {
+        while (parent[x] != x)
+        {
+            parent[x] = parent[parent[x]];
+            x = parent[x];
+        }
+        return x;
+    }
+
+    void unite(int a, int b)
+    {
+        int ra = find(a);
+        int rb = find(b);
+        if (ra == rb) return;
+
+        if (rank[ra] < rank[rb])
+        {
+            parent[ra] = rb;
+        }
+        else if (rank[ra] > rank[rb])
+        {
+            parent[rb] = ra;
+        }
+        else
+        {
+            parent[rb] = ra;
+            rank[ra]++;
+        }
+    }
+
+    foreach (ref stone; dominoes)
+    {
+        tally[stone.left]++;
+        tally[stone.right]++;
+        unite(stone.left, stone.right);
+    }
+
+    // All vertices must have even tally
+    foreach (t; tally)
+        if (t % 2 != 0) return false;
+
+    // At most one connected component among vertices with nonzero tally
+    int roots = 0;
+    foreach (i; 0 .. n)
+        if (tally[i] > 0 && parent[i] == i)
+            roots++;
+
+    return roots <= 1;
+}

exercises/practice/dominoes/source/dominoes.d

@@ -0,0 +1,97 @@
+module dominoes;
+
+struct Stone {
+    int left;
+    int right;
+}
+
+pure bool canChain(immutable Stone[] dominoes)
+{
+    // implement this function
+}
+
+unittest
+{
+    immutable int allTestsEnabled = 0;
+
+    // Empty input = empty output
+    {
+        immutable Stone[] dominoes;
+        assert(canChain(dominoes));
+    }
+
+    static if (allTestsEnabled)
+    {
+        // Singleton input = singleton output
+        {
+            immutable Stone[] dominoes = [Stone(1, 1)];
+            assert(canChain(dominoes));
+        }
+
+        // Singleton that can't be chained
+        {
+            immutable Stone[] dominoes = [Stone(1, 2)];
+            assert(!canChain(dominoes));
+        }
+
+        // Three elements
+        {
+            immutable Stone[] dominoes = [Stone(1, 2), Stone(3, 1), Stone(2, 3)];
+            assert(canChain(dominoes));
+        }
+
+        // Can reverse dominoes
+        {
+            immutable Stone[] dominoes = [Stone(1, 2), Stone(1, 3), Stone(2, 3)];
+            assert(canChain(dominoes));
+        }
+
+        // Can't be chained
+        {
+            immutable Stone[] dominoes = [Stone(1, 2), Stone(4, 1), Stone(2, 3)];
+            assert(!canChain(dominoes));
+        }
+
+        // Disconnected - simple
+        {
+            immutable Stone[] dominoes = [Stone(1, 1), Stone(2, 2)];
+            assert(!canChain(dominoes));
+        }
+
+        // Disconnected - double loop
+        {
+            immutable Stone[] dominoes = [Stone(1, 2), Stone(2, 1), Stone(3, 4), Stone(4, 3)];
+            assert(!canChain(dominoes));
+        }
+
+        // Disconnected - single isolated
+        {
+            immutable Stone[] dominoes = [Stone(1, 2), Stone(2, 3), Stone(3, 1), Stone(4, 4)];
+            assert(!canChain(dominoes));
+        }
+
+        // Need backtrack
+        {
+            immutable Stone[] dominoes = [Stone(1, 2), Stone(2, 3), Stone(3, 1), Stone(2, 4), Stone(2, 4)];
+            assert(canChain(dominoes));
+        }
+
+        // Separate loops
+        {
+            immutable Stone[] dominoes = [Stone(1, 2), Stone(2, 3), Stone(3, 1), Stone(1, 1), Stone(2, 2), Stone(3, 3)];
+            assert(canChain(dominoes));
+        }
+
+        // Nine elements
+        {
+            immutable Stone[] dominoes = [Stone(1, 2), Stone(5, 3), Stone(3, 1), Stone(1, 2), Stone(2, 4), Stone(1, 6), Stone(2, 3), Stone(3, 4), Stone(5, 6)];
+            assert(canChain(dominoes));
+        }
+
+        // Separate three-domino loops
+        {
+            immutable Stone[] dominoes = [Stone(1, 2), Stone(2, 3), Stone(3, 1), Stone(4, 5), Stone(5, 6), Stone(6, 4)];
+            assert(!canChain(dominoes));
+        }
+    }
+}