Day 19 done.

Author: jwcarman

src/main/kotlin/adventofcode/day19/LinenLayout.kt

@@ -0,0 +1,48 @@
+/*
+ * Copyright (c) 2025 James Carman
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package adventofcode.day19
+
+import adventofcode.util.splitByEmptyLines
+import adventofcode.util.trie.Trie
+
+fun String.parseTowelsAndPatterns(): Pair<Trie, List<String>> {
+    val (towelInput, patternInput) = splitByEmptyLines()
+    val towels = towelInput.split(", ").toSet()
+    val patterns = patternInput.lines()
+    val trie = Trie()
+    towels.forEach { trie.insert(it) }
+    return trie to patterns
+}
+
+fun String.countPossibleDesigns(): Int {
+    val (trie, patterns) = parseTowelsAndPatterns()
+    val memory = mutableMapOf<String, Long>()
+    return patterns.count { countPossibleCombos(it, trie, memory) > 0L }
+}
+
+fun String.countDesignCombos(): Long {
+    val (trie, patterns) = parseTowelsAndPatterns()
+    val memory = mutableMapOf<String, Long>()
+    return patterns.sumOf { pattern -> countPossibleCombos(pattern, trie, memory) }
+}
+
+fun countPossibleCombos(pattern: String, trie: Trie, memory: MutableMap<String, Long>): Long {
+    return memory.getOrPut(pattern) {
+        trie.prefixesOf(pattern)
+            .sumOf { if (it == pattern) 1L else countPossibleCombos(pattern.removePrefix(it), trie, memory) }
+    }
+}

src/main/kotlin/adventofcode/util/trie/Trie.kt

@@ -0,0 +1,67 @@
+/*
+ * Copyright (c) 2025 James Carman
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package adventofcode.util.trie
+
+class Trie {
+
+    private val root: TrieNode = TrieNode("")
+
+    fun insert(word: String) {
+        var current = root
+        for (char in word) {
+            current = current.children.getOrPut(char) { TrieNode(current.prefix + char) }
+        }
+        current.isEndOfWord = true
+    }
+
+    fun prefixesOf(word: String): List<String> {
+        var current = root
+        val prefixes = mutableListOf<String>()
+        for (char in word) {
+            if (current.isEndOfWord) {
+                prefixes.add(current.prefix)
+            }
+            current = current.children[char] ?: return prefixes
+        }
+        if (current.isEndOfWord) {
+            prefixes.add(current.prefix)
+        }
+
+        return prefixes
+    }
+
+    fun search(word: String): Boolean {
+        var current = root
+        for (char in word) {
+            current = current.children[char] ?: return false
+        }
+        return current.isEndOfWord
+    }
+
+    fun startsWith(prefix: String): Boolean {
+        var current = root
+        for (char in prefix) {
+            current = current.children[char] ?: return false
+        }
+        return true
+    }
+}
+
+private class TrieNode(val prefix: String) {
+    val children: MutableMap<Char, TrieNode> = mutableMapOf()
+    var isEndOfWord: Boolean = false
+}

src/test/kotlin/adventofcode/Day19Test.kt

@@ -16,32 +16,34 @@
 
 package adventofcode
 
+import adventofcode.day19.countPossibleDesigns
+import adventofcode.day19.countDesignCombos
 import io.kotest.matchers.shouldBe
 import org.junit.jupiter.api.Test
 
 class Day19Test {
 
     @Test
     fun example1() {
-        calculatePart1(readExample1()) shouldBe 0
+        calculatePart1(readExample1()) shouldBe 6
     }
 
     @Test
     fun part1() {
-        calculatePart1(readInput()) shouldBe 0
+        calculatePart1(readInput()) shouldBe 206
     }
 
     @Test
     fun example2() {
-        calculatePart2(readExample2()) shouldBe 0
+        calculatePart2(readExample2()) shouldBe 16L
     }
 
     @Test
     fun part2() {
-        calculatePart2(readInput()) shouldBe 0
+        calculatePart2(readInput()) shouldBe 622121814629343L
     }
 
-    private fun calculatePart1(input: String): Int = 0
+    private fun calculatePart1(input: String): Int = input.countPossibleDesigns()
 
-    private fun calculatePart2(input: String): Int = 0
+    private fun calculatePart2(input: String): Long = input.countDesignCombos()
 }

src/test/kotlin/adventofcode/util/trie/TrieTest.kt

@@ -0,0 +1,17 @@
+package adventofcode.util.trie
+
+import io.kotest.matchers.shouldBe
+import org.junit.jupiter.api.Test
+
+class TrieTest {
+    @Test
+    fun `single letter should be a valid prefix`() {
+        val trie = Trie()
+        trie.insert("r")
+        trie.insert("ru")
+        trie.insert("hello")
+        trie.insert("ruf")
+        trie.insert("ruff")
+        trie.prefixesOf("ruff") shouldBe listOf("r", "ru", "ruf", "ruff")
+    }
+}

src/test/resources/day19-example1.txt

@@ -0,0 +1,10 @@
+r, wr, b, g, bwu, rb, gb, br
+
+brwrr
+bggr
+gbbr
+rrbgbr
+ubwu
+bwurrg
+brgr
+bbrgwb

src/test/resources/day19-example2.txt

@@ -0,0 +1,10 @@
+r, wr, b, g, bwu, rb, gb, br
+
+brwrr
+bggr
+gbbr
+rrbgbr
+ubwu
+bwurrg
+brgr
+bbrgwb