Solution Day 21, part two (Keypad Conundrum)

Author: rhaendel

src/main/kotlin/de/ronny_h/aoc/year24/day21/KeypadConundrum.kt

@@ -7,38 +7,35 @@ import de.ronny_h.aoc.extensions.SimpleCharGrid
 import de.ronny_h.aoc.extensions.asList
 import de.ronny_h.aoc.extensions.memoize
 
-fun main() = KeypadConundrum().run(94426, 0)
+fun main() = KeypadConundrum().run(94426, 118392478819140)
 
-class KeypadConundrum : AdventOfCode<Int>(2024, 21) {
-    fun input(code: String, keypad: Keypad, depth: Int): String {
+class KeypadConundrum : AdventOfCode<Long>(2024, 21) {
+    fun input(code: String, keypad: Keypad, depth: Int): Long {
         data class Parameters(val code: String, val depth: Int)
 
-        val keypads = buildList(depth) {
-            repeat(depth) { add(Keypad(directionalKeypadLayout)) }
-        } + keypad
-        lateinit var inputRec: (Parameters) -> String
+        val keypads = List(depth) { Keypad(directionalKeypadLayout) } + keypad
+        lateinit var inputRec: (Parameters) -> Long
 
         inputRec = { p: Parameters ->
             if (p.depth == 0) {
-                p.code
+                p.code.length.toLong()
             } else {
                 p.code.map { char ->
-                    keypads[p.depth].moveTo(char).map {
+                    keypads[p.depth].moveTo(char).minOf {
                         inputRec(Parameters(it, p.depth - 1))
-                    }.minBy { it.length }
-                }.joinToString("")
+                    }
+                }.sum()
             }
         }.memoize()
 
         return inputRec(Parameters(code, depth))
     }
 
-    override fun part1(input: List<String>): Int = input.sumOf {
-        input(it, Keypad(numericKeypadLayout), 3).length * it.dropLast(1).toInt()
-    }
+    override fun part1(input: List<String>): Long = sumOfComplexities(input, 3)
+    override fun part2(input: List<String>): Long = sumOfComplexities(input, 26)
 
-    override fun part2(input: List<String>): Int = input.sumOf {
-        input(it, Keypad(numericKeypadLayout), 26).length * it.dropLast(1).toInt()
+    private fun sumOfComplexities(input: List<String>, depth: Int): Long = input.sumOf { code ->
+        input(code, Keypad(numericKeypadLayout), depth) * code.dropLast(1).toLong()
     }
 }
 

src/test/kotlin/de/ronny_h/aoc/year24/day21/KeypadConundrumTest.kt

@@ -2,7 +2,6 @@ package de.ronny_h.aoc.year24.day21
 
 import de.ronny_h.aoc.extensions.asList
 import io.kotest.core.spec.style.StringSpec
-import io.kotest.matchers.collections.shouldBeIn
 import io.kotest.matchers.collections.shouldContainExactlyInAnyOrder
 import io.kotest.matchers.shouldBe
 
@@ -32,23 +31,15 @@ class KeypadConundrumTest : StringSpec({
     }
 
     "input v<<A>>^A, last robot" {
-        KeypadConundrum().input("v<<A>>^A", Keypad(directionalKeypadLayout), 1) shouldBeIn
-                listOf(
-                    "<vA<AA>>^AvAA<^A>A",
-                    "v<A<AA>^>AvAA^<A>A",
-                    )
+        KeypadConundrum().input("v<<A>>^A", Keypad(directionalKeypadLayout), 1) shouldBe 18L
     }
 
     "input 0, all robots" {
-        KeypadConundrum().input("0", Keypad(numericKeypadLayout), 3) shouldBeIn
-                listOf(
-                    "<vA<AA>>^AvAA<^A>A",
-                    "v<A<AA>^>AvAA^<A>A",
-                )
+        KeypadConundrum().input("0", Keypad(numericKeypadLayout), 3) shouldBe 18L
     }
 
     "input with depth 1" {
-        KeypadConundrum().input("v", Keypad(directionalKeypadLayout), 1) shouldBe "v<A"
+        KeypadConundrum().input("v", Keypad(directionalKeypadLayout), 1) shouldBe 3
     }
 
     "part 1: The sum of the complexities of the five codes" {