Day 19

Author: WVerlaek

src/main/kotlin/y24/Day19.kt

@@ -0,0 +1,70 @@
+package y24
+
+import common.puzzle.solvePuzzle
+import common.puzzle.Input
+import common.puzzle.Puzzle
+
+
+fun main() = solvePuzzle(year = 2024, day = 19) { Day19(it) }
+
+class Day19(val input: Input) : Puzzle {
+    private val patterns = input.lines[0].split(", ")
+    private val designs = input.lines.subList(2, input.lines.size)
+
+    data class TrieNode(
+        val c: Char,
+        val children: MutableMap<Char, TrieNode> = mutableMapOf(),
+        var pattern: String? = null,
+    )
+
+    private fun buildTrie(patterns: List<String>): TrieNode {
+        val root = TrieNode('-')
+        patterns.forEach { pattern ->
+            var node = root
+            pattern.forEach { c ->
+                node = node.children[c] ?: TrieNode(c).also { node.children[c] = it }
+            }
+            node.pattern = pattern
+        }
+
+        return root
+    }
+
+    private fun numPossibilities(design: String, trie: TrieNode, cache: MutableMap<String, Long>): Long {
+        if (design.isEmpty()) {
+            return 1
+        }
+
+        cache[design]?.let { return it }
+
+        var node = trie
+        var i = 0
+        var num = 0L
+        while (i < design.length) {
+            val c = design[i]
+            i++
+
+            node = node.children[c] ?: run {
+                cache[design] = num
+                return num
+            }
+
+            node.pattern?.let {
+                num += numPossibilities(design.substring(i), trie, cache)
+            }
+        }
+
+        cache[design] = num
+        return num
+    }
+
+    override fun solveLevel1(): Any {
+        val trie = buildTrie(patterns)
+        return designs.count { design -> numPossibilities(design, trie, mutableMapOf()) > 0 }
+    }
+
+    override fun solveLevel2(): Any {
+        val trie = buildTrie(patterns)
+        return designs.sumOf { design -> numPossibilities(design, trie, mutableMapOf()) }
+    }
+}

src/test/kotlin/y24/Day19Test.kt

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+package y24
+
+import common.puzzle.Input
+import org.junit.jupiter.api.Assertions.assertEquals
+import org.junit.jupiter.api.Test
+
+internal class Day19Test {
+    private val sample = Input("""
+    r, wr, b, g, bwu, rb, gb, br
+    
+    brwrr
+    bggr
+    gbbr
+    rrbgbr
+    ubwu
+    bwurrg
+    brgr
+    bbrgwb
+    """.trimIndent())
+
+    private val day = Day19(sample)
+
+    @Test
+    fun solveLevel1() {
+        assertEquals(6, day.solveLevel1())
+    }
+
+    @Test
+    fun solveLevel2() {
+         assertEquals(16L, day.solveLevel2())
+    }
+}