Solution 2017-12 (Digital Plumber)

Author: rhaendel

src/main/kotlin/de/ronny_h/aoc/year2017/day12/DigitalPlumber.kt

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+package de.ronny_h.aoc.year2017.day12
+
+import de.ronny_h.aoc.AdventOfCode
+
+fun main() = DigitalPlumber().run(134, 193)
+
+class DigitalPlumber : AdventOfCode<Int>(2017, 12) {
+    override fun part1(input: List<String>): Int = input.parseDirectConnections().groupOf(0).size
+
+    override fun part2(input: List<String>): Int {
+        val connections = input.parseDirectConnections()
+
+        val groups = mutableListOf<List<Int>>()
+        connections.keys.forEach { programId ->
+            if (groups.none { it.contains(programId) }) {
+                groups.add(connections.groupOf(programId))
+            }
+        }
+
+        return groups.size
+    }
+
+    private fun List<String>.parseDirectConnections(): Map<Int, List<Int>> = associate {
+        val (programId, connections) = it.split(" <-> ")
+        programId.toInt() to connections.split(", ").map(String::toInt)
+    }
+
+    private fun Map<Int, List<Int>>.groupOf(start: Int): List<Int> {
+        val group = mutableListOf(start)
+        fun addTransitiveConnectionsOf(programId: Int) {
+            this[programId]?.forEach {
+                if (!group.contains(it)) {
+                    group.add(it)
+                    addTransitiveConnectionsOf(it)
+                }
+            }
+        }
+        addTransitiveConnectionsOf(start)
+        return group
+    }
+}

src/test/kotlin/de/ronny_h/aoc/year2017/day12/DigitalPlumberTest.kt

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+package de.ronny_h.aoc.year2017.day12
+
+import de.ronny_h.aoc.extensions.asList
+import io.kotest.core.spec.style.StringSpec
+import io.kotest.matchers.shouldBe
+
+class DigitalPlumberTest : StringSpec({
+
+    val input = """
+        0 <-> 2
+        1 <-> 1
+        2 <-> 0, 3, 4
+        3 <-> 2, 4
+        4 <-> 2, 3, 6
+        5 <-> 6
+        6 <-> 4, 5
+    """.asList()
+
+    "part 1: the number of programs in the group that contains program ID 0" {
+        DigitalPlumber().part1(input) shouldBe 6
+    }
+
+    "part 2: the number of groups in total" {
+        DigitalPlumber().part2(input) shouldBe 2
+    }
+})