Day 13

aoc/src/dev/ctsk/aoc/Main.scala

@@ -14,7 +14,8 @@ val solvers = Map[Int, Solver](
   9 -> Day09,
   10 -> Day10,
   11 -> Day11,
-  12 -> Day12
+  12 -> Day12,
+  13 -> Day13
 )
 
 def runSolver(solver: Solver, input: os.Path): Unit =

aoc/src/dev/ctsk/aoc/days/Day13.scala

@@ -0,0 +1,42 @@
+package dev.ctsk.aoc.days
+
+import dev.ctsk.aoc.*
+import os.ReadablePath
+
+object Day13 extends Solver(13):
+  def solve(machine: Vector[Long], error: Long = 0): Option[(Long, Long)] =
+    val Vector(ax, ay, bx, by, px, py) = machine
+    val px_adj = px + error
+    val py_adj = py + error
+    val j = (py_adj * ax - px_adj * ay) / (ax * by - bx * ay)
+    val i = (px_adj * by - py_adj * bx) / (ax * by - bx * ay)
+
+    if i * ax + j * bx == px_adj && i * ay + j * by == py_adj
+    then Some((i, j))
+    else None
+
+  override def run(input: ReadablePath): (Timings, Solution) =
+    val data = os.read(input).mkString
+    val (pre_time, machines) = timed { data.split("\n\n").map(longs) }
+
+    def inRange(i: Long, j: Long) =
+      (0 to 100 contains i) && (0 to 100 contains j)
+
+    val (p1_time, p1) = timed {
+      machines
+        .map(solve(_, 0L))
+        .collect { case Some(i, j) if inRange(i, j) => i * 3 + j }
+        .sum
+    }
+
+    val (p2_time, p2) = timed {
+      machines
+        .map(solve(_, 10000000000000L))
+        .collect { case Some(i, j) => i * 3 + j }
+        .sum
+    }
+
+    (
+      Timings(pre_time, p1_time, p2_time),
+      Solution(Long.box(p1), Long.box(p2))
+    )

data/13.ans

@@ -0,0 +1,2 @@
+35574
+80882098756071