From 453db1c29a1aa73a956eaa0fe5d345eb19d82dbb Mon Sep 17 00:00:00 2001
From: Brian Peck <Catbert321@gmail.com>
Date: Sun, 22 Dec 2024 22:12:43 -0800
Subject: [PATCH] Day 23 2024 (#287)

---
 .../peckb/aoc/_2024/calendar/day23/Day23.kt   | 71 +++++++++++++++++++
 .../peckb/aoc/_2024/calendar/day23/README.md  |  1 +
 .../me/peckb/aoc/_2024/TestDayComponent.kt    |  2 +
 .../aoc/_2024/calendar/day23/Day23Test.kt     | 32 +++++++++
 4 files changed, 106 insertions(+)
 create mode 100644 src/main/kotlin/me/peckb/aoc/_2024/calendar/day23/Day23.kt
 create mode 100644 src/main/kotlin/me/peckb/aoc/_2024/calendar/day23/README.md
 create mode 100644 src/test/kotlin/me/peckb/aoc/_2024/calendar/day23/Day23Test.kt

diff --git a/src/main/kotlin/me/peckb/aoc/_2024/calendar/day23/Day23.kt b/src/main/kotlin/me/peckb/aoc/_2024/calendar/day23/Day23.kt
new file mode 100644
index 00000000..6ee84167
--- /dev/null
+++ b/src/main/kotlin/me/peckb/aoc/_2024/calendar/day23/Day23.kt
@@ -0,0 +1,71 @@
+package me.peckb.aoc._2024.calendar.day23
+
+import javax.inject.Inject
+import me.peckb.aoc.generators.InputGenerator.InputGeneratorFactory
+
+class Day23 @Inject constructor(
+  private val generatorFactory: InputGeneratorFactory,
+) {
+  fun partOne(filename: String) = generatorFactory.forFile(filename).readAs(::connection) { input ->
+    val connections = findFriends(input)
+    val triplets = mutableSetOf<Set<String>>()
+
+    findCommonFriend(connections) { me, them, ourFriends ->
+      ourFriends.forEach { ourFriend -> triplets.add(setOf(me, them, ourFriend)) }
+    }
+
+    triplets.count { group -> group.any { it.startsWith('t') } }
+  }
+
+  fun partTwo(filename: String) = generatorFactory.forFile(filename).readAs(::connection) { input ->
+    val connections = findFriends(input)
+    val friends = mutableSetOf<Set<String>>()
+
+    findCommonFriend(connections) { me, them, ourFriends ->
+      if (ourFriends.isNotEmpty()) {
+        val everyFriend = ourFriends.all { maybeMutual ->
+          ourFriends.minus(maybeMutual).all {
+            (maybeMutual in connections[it]!!)
+          }
+        }
+        if (everyFriend) {
+          friends.add(ourFriends.plus(me).plus(them))
+        }
+      }
+    }
+
+    friends.maxBy { it.size }.toList().sorted().joinToString(",")
+  }
+
+  private fun connection(line: String) : Pair<String, String> {
+    return line.split("-").let { (a, b) -> a to b }
+  }
+
+  private fun findFriends(input: Sequence<Pair<String, String>>): MutableMap<String, Set<String>> {
+    val connections = mutableMapOf<String, Set<String>>()
+
+    input.forEach { (c1, c2) ->
+      connections.merge(c1, setOf(c2)) { a, b -> a + b }
+      connections.merge(c2, setOf(c1)) { a, b -> a + b }
+    }
+
+    return connections
+  }
+
+  private fun findCommonFriend(connections: Map<String, Set<String>>, handleFriends: (String, String, Set<String>) -> Unit) {
+    val keys = connections.keys.toList()
+    (0 until keys.size - 2).forEach { i ->
+      val me = keys[i]
+      val myFriends = connections[me]!!
+
+      (i + 1 until keys.size - 1).forEach { j ->
+        val them = keys[j]
+        val theirFriends = connections[them]!!
+
+        if (me in theirFriends) {
+          handleFriends(me, them, myFriends.intersect(theirFriends))
+        }
+      }
+    }
+  }
+}
diff --git a/src/main/kotlin/me/peckb/aoc/_2024/calendar/day23/README.md b/src/main/kotlin/me/peckb/aoc/_2024/calendar/day23/README.md
new file mode 100644
index 00000000..5ffa3cb4
--- /dev/null
+++ b/src/main/kotlin/me/peckb/aoc/_2024/calendar/day23/README.md
@@ -0,0 +1 @@
+## [Day 23: LAN Party](https://adventofcode.com/2024/day/23)
\ No newline at end of file
diff --git a/src/test/kotlin/me/peckb/aoc/_2024/TestDayComponent.kt b/src/test/kotlin/me/peckb/aoc/_2024/TestDayComponent.kt
index e3e16447..ec833387 100644
--- a/src/test/kotlin/me/peckb/aoc/_2024/TestDayComponent.kt
+++ b/src/test/kotlin/me/peckb/aoc/_2024/TestDayComponent.kt
@@ -22,6 +22,7 @@ import me.peckb.aoc._2024.calendar.day19.Day19Test
 import me.peckb.aoc._2024.calendar.day20.Day20Test
 import me.peckb.aoc._2024.calendar.day21.Day21Test
 import me.peckb.aoc._2024.calendar.day22.Day22Test
+import me.peckb.aoc._2024.calendar.day23.Day23Test
 import javax.inject.Singleton
 import me.peckb.aoc.DayComponent
 import me.peckb.aoc.InputModule
@@ -52,4 +53,5 @@ internal interface TestDayComponent : DayComponent {
   fun inject(day20Test: Day20Test)
   fun inject(day21Test: Day21Test)
   fun inject(day22Test: Day22Test)
+  fun inject(day23Test: Day23Test)
 }
diff --git a/src/test/kotlin/me/peckb/aoc/_2024/calendar/day23/Day23Test.kt b/src/test/kotlin/me/peckb/aoc/_2024/calendar/day23/Day23Test.kt
new file mode 100644
index 00000000..b0fb7250
--- /dev/null
+++ b/src/test/kotlin/me/peckb/aoc/_2024/calendar/day23/Day23Test.kt
@@ -0,0 +1,32 @@
+package me.peckb.aoc._2024.calendar.day23
+
+import javax.inject.Inject
+
+import me.peckb.aoc._2024.DaggerTestDayComponent
+import org.junit.jupiter.api.Assertions.assertEquals
+import org.junit.jupiter.api.BeforeEach
+import org.junit.jupiter.api.Test
+
+internal class Day23Test {
+  @Inject
+  lateinit var day23: Day23
+
+  @BeforeEach
+  fun setup() {
+    DaggerTestDayComponent.create().inject(this)
+  }
+
+  @Test
+  fun testDay23PartOne() {
+    assertEquals(998, day23.partOne(DAY_23))
+  }
+
+  @Test
+  fun testDay23PartTwo() {
+    assertEquals("cc,ff,fh,fr,ny,oa,pl,rg,uj,wd,xn,xs,zw", day23.partTwo(DAY_23))
+  }
+
+  companion object {
+    private const val DAY_23: String = "advent-of-code-input/2024/day23.input"
+  }
+}