Day 11

Author: WVerlaek

src/main/kotlin/y25/Day11.kt

@@ -0,0 +1,84 @@
+package y25
+
+import com.google.common.graph.Graph
+import com.google.common.graph.GraphBuilder
+import com.google.common.graph.Graphs
+import common.puzzle.solvePuzzle
+import common.puzzle.Input
+import common.puzzle.Puzzle
+import common.datastructures.*
+import common.ext.*
+import common.util.*
+import java.util.*
+import kotlin.math.*
+import kotlin.system.exitProcess
+
+
+fun main() = solvePuzzle(year = 2025, day = 11) { Day11(it) }
+
+@Suppress("UnstableApiUsage")
+class Day11(val input: Input) : Puzzle {
+
+    private fun parseInput(): Graph<String> {
+        val graph = GraphBuilder<String>.directed().build<String>()
+
+        input.lines.forEach { line ->
+            val (node, outputs) = line.split(": ")
+            val outputNodes = outputs.split(" ")
+            outputNodes.forEach { outputNode ->
+                graph.putEdge(node, outputNode)
+            }
+        }
+
+        return graph
+    }
+
+    data class Memoized(
+        val node: String,
+        val missingNodes: Set<String>,
+    )
+
+    private fun Graph<String>.pathsToNode(
+        from: String,
+        target: String,
+        requiredNodes: MutableSet<String>,
+        visited: MutableSet<String> = mutableSetOf(),
+        cache: MutableMap<Memoized, Long> = mutableMapOf(),
+    ): Long {
+        if (from == target) return if (requiredNodes.isEmpty()) 1 else 0
+
+        if (from in visited) {
+            // Found cycle, ignore.
+            return 0
+        }
+        visited += from
+
+        var addBack = false
+        if (from in requiredNodes) {
+            requiredNodes -= from
+            addBack = true
+        }
+
+        val memo = Memoized(from, requiredNodes.toSet())
+        val result = cache[memo] ?: successors(from).sumOf { neigh ->
+            pathsToNode(neigh, target, requiredNodes, visited, cache)
+        }.also { cache[memo] = it }
+
+        if (addBack) {
+            requiredNodes += from
+        }
+        visited -= from
+
+        return result
+    }
+
+    override fun solveLevel1(): Any {
+        val graph = parseInput()
+        return graph.pathsToNode("you", "out", mutableSetOf())
+    }
+
+    override fun solveLevel2(): Any {
+        val graph = parseInput()
+        return graph.pathsToNode("svr", "out", mutableSetOf("dac", "fft"))
+    }
+}

src/test/kotlin/y25/Day11Test.kt

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+package y25
+
+import common.puzzle.Input
+import org.junit.jupiter.api.Assertions.assertEquals
+import org.junit.jupiter.api.Test
+
+internal class Day11Test {
+    private val sample = Input("""
+aaa: you hhh
+you: bbb ccc
+bbb: ddd eee
+ccc: ddd eee fff
+ddd: ggg
+eee: out
+fff: out
+ggg: out
+hhh: ccc fff iii
+iii: out
+    """.trimIndent())
+
+    private val day = Day11(sample)
+
+    @Test
+    fun solveLevel1() {
+        assertEquals(5L, day.solveLevel1())
+    }
+
+    @Test
+    fun solveLevel2() {
+         assertEquals(2L, Day11(Input("""
+             svr: aaa bbb
+             aaa: fft
+             fft: ccc
+             bbb: tty
+             tty: ccc
+             ccc: ddd eee
+             ddd: hub
+             hub: fff
+             eee: dac
+             dac: fff
+             fff: ggg hhh
+             ggg: out
+             hhh: out
+         """.trimIndent())).solveLevel2())
+    }
+}