Add Day 13

build.gradle.kts

@@ -11,6 +11,8 @@ repositories {
 
 dependencies {
     testImplementation(kotlin("test"))
+    implementation("org.jetbrains.kotlinx:multik-core:0.2.3")
+    implementation("org.jetbrains.kotlinx:multik-default:0.2.3")
 }
 
 tasks.test {

src/main/kotlin/Day13.kt

@@ -0,0 +1,48 @@
+import kotlin.math.abs
+import kotlin.math.round
+import org.jetbrains.kotlinx.multik.api.linalg.solve
+import org.jetbrains.kotlinx.multik.api.mk
+import org.jetbrains.kotlinx.multik.api.ndarray
+import org.jetbrains.kotlinx.multik.ndarray.operations.first
+import org.jetbrains.kotlinx.multik.ndarray.operations.last
+import utils.AoCDay
+import utils.mapToLong
+
+class Day13 : AoCDay() {
+    val splits = input.joinToString("\n").split("\n\n")
+        .map { it.split("\n").map { it.split(": ")[1].split(", ").map { it.drop(2) }.mapToLong() } }
+    val validDistance = 0.01
+
+    override fun part1(): Any {
+        return splits.sumOf { split ->
+            val buttonA = split[0]
+            val buttonB = split[1]
+            val prize = split[2]
+            calculateCost(buttonA, buttonB, prize)
+        }
+    }
+
+    override fun part2(): Any {
+        return splits.sumOf { split ->
+            val buttonA = split[0]
+            val buttonB = split[1]
+            val prize = split[2].map { it + 10000000000000 }
+            calculateCost(buttonA, buttonB, prize)
+        }
+    }
+
+    fun calculateCost(buttonA: List<Long>, buttonB: List<Long>, prize: List<Long>): Long {
+        val buttons = mk.ndarray(listOf(listOf(buttonA[0], buttonB[0]), listOf(buttonA[1], buttonB[1])))
+        val result = mk.linalg.solve(buttons, mk.ndarray(prize))
+        // println(result)
+        if (abs(result.first() - round(result.first())) > validDistance || abs(result.last() - round(result.last())) > validDistance) {
+            // println("Invalid result: $result")
+            return 0
+        }
+        return round(result.first()).toLong() * 3 + round(result.last()).toLong()
+    }
+}
+
+fun main() {
+    Day13().execute()
+}