From e720bbecdbafa15584537da9adf7a85e9d91cfce Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Fredrik=20R=C3=B8dland?= <fmr@finn.no>
Date: Fri, 15 Dec 2023 10:38:20 +0100
Subject: [PATCH] 2023 - Day 15 - part 2

---
 .../kotlin/no/rodland/advent_2023/Day15.kt    | 53 ++++++++++++++++---
 .../no/rodland/advent_2023/Day15Test.kt       |  4 +-
 2 files changed, 48 insertions(+), 9 deletions(-)

diff --git a/src/main/kotlin/no/rodland/advent_2023/Day15.kt b/src/main/kotlin/no/rodland/advent_2023/Day15.kt
index d8f0abac..14debf32 100644
--- a/src/main/kotlin/no/rodland/advent_2023/Day15.kt
+++ b/src/main/kotlin/no/rodland/advent_2023/Day15.kt
@@ -5,24 +5,63 @@ import no.rodland.advent.Day
 // template generated: 15/12/2023
 // Fredrik Rødland 2023
 
-class Day15(val input: List<String>) : Day<Int, Long, List<CharArray>> {
+class Day15(val input: List<String>) : Day<Int, Int, List<Day15.Step>> {
 
     private val parsed = input.parse()
 
     override fun partOne(): Int {
-        return parsed.sumOf { it.hash() }
+        return parsed.sumOf { it.hash }
     }
 
-    private fun CharArray.hash() = fold(0) { acc, c -> ((c.code + acc) * 17).mod(256) }
+    override fun partTwo(): Int {
+        val ar = Array(256) { mutableListOf<Lens>() }
+        parsed.forEach { step ->
+            ar[step.label.hash()].also { box ->
+                if (step.isMinus) {
+                    box.remove(step.label)
+                } else {
+                    box.replace(step.label, step)
+                }
+            }
+        }
+        return ar.flatMapIndexed { idx, list ->
+            list.mapIndexed { listIdx, lens -> focusingPower(idx, listIdx, lens) }
+        }.sum()
+    }
+
+    private fun focusingPower(boxIndex: Int, lensIndex: Int, lens: Lens) = (boxIndex + 1) * (lensIndex + 1) * lens.focal
+
+    private fun MutableList<Lens>.remove(label: String) {
+        removeAll { it.label == label }
+    }
 
-    override fun partTwo(): Long {
-        return 2
+    private fun MutableList<Lens>.replace(label: String, step: Step) {
+        Lens(label, step.num!!).also { lens ->
+            indexOfFirst { it.label == label }.also { if (it >= 0) this[it] = lens else add(lens) }
+        }
     }
 
-    override fun List<String>.parse(): List<CharArray> {
-        return first().split(",").map { it.toCharArray() }
+    data class Lens(val label: String, val focal: Int)
+
+    data class Step(val str: String) {
+        val label = str.split("=", "-")[0]
+        val num: Int? = str.split("=").let {
+            if (it.size == 2) {
+                it[1].toInt()
+            } else {
+                null
+            }
+        }
+        val isMinus = num == null
+        val hash = str.hash()
+    }
+
+    override fun List<String>.parse(): List<Step> {
+        return first().split(",").map { Step(it) }
     }
 
     override val day = "15".toInt()
 }
 
+fun String.hash() = fold(0) { acc, c -> ((c.code + acc) * 17).mod(256) }
+
diff --git a/src/test/kotlin/no/rodland/advent_2023/Day15Test.kt b/src/test/kotlin/no/rodland/advent_2023/Day15Test.kt
index 6bcd5a6b..56814890 100644
--- a/src/test/kotlin/no/rodland/advent_2023/Day15Test.kt
+++ b/src/test/kotlin/no/rodland/advent_2023/Day15Test.kt
@@ -16,9 +16,9 @@ internal class Day15Test {
     private val test15 = "2023/input_15_test.txt".readFile()
 
     private val resultTestOne = 1320
-    private val resultTestTwo = 2L
+    private val resultTestTwo = 145
     private val resultOne = 522547
-    private val resultTwo = 2L
+    private val resultTwo = 229271
 
     val test = defaultTestSuiteParseOnInit(
         Day15(data15),