2024 - Day 13 - part 1 & 2

src/main/kotlin/no/rodland/advent_2024/Day13.kt

@@ -1,35 +1,42 @@
 package no.rodland.advent_2024
 
 import no.rodland.advent.Day
-import no.rodland.advent.Pos
 
 // template generated: 13/12/2024
 // Fredrik Rødland 2024
 
 class Day13(val input: List<String>) : Day<Long, Long, List<Day13.Machine>> {
 
     private val machines = input.parse()
+    private val machinesPart2 = machines.map { it.copy(p = P(10000000000000L + it.p.x, 10000000000000L + it.p.y)) }
 
     override fun partOne(): Long {
-        return 2
+        return machines.filter { it.ok }.sumOf { it.ca * 3 + it.cb }
     }
 
     override fun partTwo(): Long {
-        return 2
+        return machinesPart2.filter { it.ok }.sumOf { it.ca * 3 + it.cb }
+    }
+
+    data class Machine(val a: P, val b: P, val p: P) {
+        val cb = (p.y * a.x - p.x * a.y) / (a.x * b.y - a.y * b.x)
+        val ca = (p.x - cb * b.x) / a.x
+        val ok = (cb * b.x + ca * a.x == p.x) && (cb * b.y + ca * a.y == p.y)
     }
 
     override fun List<String>.parse(): List<Machine> {
         return chunked(4).map { (a, b, p) ->
-            val ax = a.substringAfter("X+").substringBefore(",").toInt()
-            val ay = a.substringAfter("Y+").toInt()
-            val bx = b.substringAfter("X+").substringBefore(",").toInt()
-            val by = b.substringAfter("Y+").toInt()
-            val px = p.substringAfter("X=").substringBefore(",").toInt()
-            val py = p.substringAfter("Y=").toInt()
-            Machine(Pos(ax, ay), Pos(bx, by), Pos(px, py))
+            val ax = a.substringAfter("X+").substringBefore(",").toLong()
+            val ay = a.substringAfter("Y+").toLong()
+            val bx = b.substringAfter("X+").substringBefore(",").toLong()
+            val by = b.substringAfter("Y+").toLong()
+            val px = p.substringAfter("X=").substringBefore(",").toLong()
+            val py = p.substringAfter("Y=").toLong()
+            Machine(P(ax, ay), P(bx, by), P(px, py))
         }
     }
 
-    data class Machine(val a: Pos, val b: Pos, val prize: Pos)
+    data class P(val x: Long, val y: Long)
+
     override val day = "13".toInt()
 }

src/test/kotlin/no/rodland/advent_2024/Day13Test.kt

@@ -15,10 +15,10 @@ internal class Day13Test {
     private val data13 = "2024/input_13.txt".readFile()
     private val test13 = "2024/input_13_test.txt".readFile()
 
-    private val resultTestOne = 2L
-    private val resultTestTwo = 2L
-    private val resultOne = 2L
-    private val resultTwo = 2L
+    private val resultTestOne = 480L
+    private val resultTestTwo = 875318608908L
+    private val resultOne = 36954L
+    private val resultTwo = 79352015273424L
 
     val test = defaultTestSuiteParseOnInit(
         Day13(data13),