19

Author: jamOne-

src/main/kotlin/19.kt

@@ -0,0 +1,40 @@
+fun main() {
+    println(solve19a(readInputLines("19")))
+    println(solve19b(readInputLines("19")))
+}
+
+fun solve19a(lines: List<String>): Int {
+    val (designs, towels) = parseInput(lines)
+    return towels.count { countPossibleOrders(designs, it) > 0 }
+}
+
+fun solve19b(lines: List<String>): Long {
+    val (designs, towels) = parseInput(lines)
+    return towels.sumOf { countPossibleOrders(designs, it) }
+}
+
+private data class Input19(val designs: List<String>, val towels: List<String>)
+
+private fun parseInput(lines: List<String>): Input19 {
+    val designs = lines[0].split(", ")
+    val towels = lines.drop(2)
+    return Input19(designs, towels)
+}
+
+private val MEM = mutableMapOf<String, Long>()
+private fun countPossibleOrders(designs: List<String>, towels: String): Long {
+    if (towels.isEmpty()) {
+        return 1
+    }
+    if (towels !in MEM) {
+        var result = 0L
+        for (d in designs) {
+            if (towels.startsWith(d)) {
+                result += countPossibleOrders(designs, towels.removePrefix(d))
+            }
+        }
+        MEM[towels] = result
+    }
+
+    return checkNotNull(MEM[towels])
+}