Day 13 part 1

2024/src/main/kotlin/day13.kt

@@ -0,0 +1,34 @@
+val regex = "Button A: X\\+(\\d+), Y\\+(\\d+)\nButton B: X\\+(\\d+), Y\\+(\\d+)\nPrize: X=(\\d+), Y=(\\d+)".toRegex()
+
+data class Machine(
+    val buttonA: Grid.Coordinate,
+    val buttonB: Grid.Coordinate,
+    val price: Grid.Coordinate
+) {
+
+    fun solveA(b: Int) = (price.x - b * buttonB.x) / buttonA.x
+    fun solveB() = (price.y * buttonA.x - price.x * buttonA.y) / (buttonA.x * buttonB.y - buttonA.y * buttonB.x)
+
+    fun solve(): Pair<Int, Int>? {
+        val b = solveB()
+        val a = solveA(b)
+
+        return Pair(a, b).takeIf { (a * buttonA.x + b * buttonB.x) == price.x && (a * buttonA.y + b * buttonB.y) == price.y }
+    }
+}
+
+fun main() {
+    val part1 = regex.findAll(readInputString("day13.txt"))
+        .map {
+            Machine(
+                buttonA = Grid.Coordinate(it.groupValues[1].toInt(), it.groupValues[2].toInt()),
+                buttonB = Grid.Coordinate(it.groupValues[3].toInt(), it.groupValues[4].toInt()),
+                price = Grid.Coordinate(it.groupValues[5].toInt(), it.groupValues[6].toInt()),
+            )
+        }
+        .mapNotNull { it.solve() }
+        .sumOf { (a, b) -> 3 * a + b }
+
+    println("Part 1: $part1")
+
+}

2024/src/main/resources/day13-sample.txt

@@ -0,0 +1,15 @@
+Button A: X+94, Y+34
+Button B: X+22, Y+67
+Prize: X=8400, Y=5400
+
+Button A: X+26, Y+66
+Button B: X+67, Y+21
+Prize: X=12748, Y=12176
+
+Button A: X+17, Y+86
+Button B: X+84, Y+37
+Prize: X=7870, Y=6450
+
+Button A: X+69, Y+23
+Button B: X+27, Y+71
+Prize: X=18641, Y=10279