Day 23.

src/aoc2024/Day23.kt

@@ -0,0 +1,111 @@
+package aoc2024
+
+import println
+import readInput
+
+/*
+--- Day 23: LAN Party ---
+https://adventofcode.com/2024/day/23
+*/
+fun main() {
+
+    val inlineTestInput = """
+kh-tc
+qp-kh
+de-cg
+ka-co
+yn-aq
+qp-ub
+cg-tb
+vc-aq
+tb-ka
+wh-tc
+yn-cg
+kh-ub
+ta-co
+de-co
+tc-td
+tb-wq
+wh-td
+ta-ka
+td-qp
+aq-cg
+wq-ub
+ub-vc
+de-ta
+wq-aq
+wq-vc
+wh-yn
+ka-de
+kh-ta
+co-tc
+wh-qp
+tb-vc
+td-yn
+"""
+
+    fun part1(input: List<String>): Int {
+        val nodes = HashMap<String, MutableSet<String>>()
+        for (i in input) {
+            val (n1, n2) = i.split("-")
+            val e1 = nodes.getOrPut(n1) { HashSet() }
+            val e2 = nodes.getOrPut(n2) { HashSet() }
+            e1.add(n2)
+            e2.add(n1)
+        }
+        val threesomes = nodes
+            .flatMap {
+                it.value.flatMap { i1 ->
+                    it.value.filter { it != i1 }.mapNotNull { i2 ->
+                        if (nodes[i1]!!.contains(it.key) && nodes[i2]!!.contains(it.key) && nodes[i1]!!.contains(i2)) sortedSetOf(it.key, i1, i2) else null
+                    }
+                }
+            }.map { it.joinToString("-", prefix = "-") }.distinct()
+
+        return threesomes.count { it.contains("-t") }
+    }
+
+    fun bronKerbosch(nodes: Map<String, Set<String>>, r: Set<String>, p: Set<String>, x: MutableSet<String>): Set<String> {
+        if (p.isEmpty() && x.isEmpty()) {
+            return r
+        }
+        var maxClique = emptySet<String>()
+        val ptmp = p.toMutableSet()
+        for (v in p) {
+            val res = bronKerbosch(nodes, r.plus(v), ptmp.intersect(nodes[v]!!), x.intersect(nodes[v]!!).toMutableSet())
+            if (res.size > maxClique.size) {
+                maxClique = res
+            }
+            ptmp.remove(v)
+            x.add(v)
+        }
+        return maxClique
+    }
+
+    fun part2(input: List<String>): String {
+        val nodes = HashMap<String, MutableSet<String>>()
+        for (i in input) {
+            val (n1, n2) = i.split("-")
+            val e1 = nodes.getOrPut(n1) { HashSet() }
+            val e2 = nodes.getOrPut(n2) { HashSet() }
+            e1.add(n2)
+            e2.add(n1)
+        }
+        val largestSet = bronKerbosch(nodes, emptySet(), nodes.keys, mutableSetOf())
+        return largestSet.asSequence().sorted().joinToString(",")
+    }
+
+    // test if implementation meets criteria from the description, like:
+    val testInput = inlineTestInput.trim().reader().readLines()
+    //val testInput = readInput("aoc2024/Day23_test")
+    val testInputPart1Result = part1(testInput)
+    println("Part 1 Test: $testInputPart1Result")
+    val testInputPart2Result = part2(testInput)
+    println("Part 2 Test: $testInputPart2Result")
+    check(testInputPart1Result == 7)
+    check(testInputPart2Result == "co,de,ka,ta")
+
+    val input = readInput("aoc2024/Day23")
+    part1(input).println()
+    part2(input).println()
+}