Day 15

aoc/src/Day15.scala

@@ -0,0 +1,76 @@
+import scala.io.Source
+import scala.util.chaining.*
+
+object Day15 extends App:
+
+  val input = Source
+    .fromURL(getClass.getResource("day15Input.txt"))
+    .mkString
+    .split('\n')
+    .map(
+      _.drop(12)
+        .split(": closest beacon is at x=")
+        .map(_.split(", y=").map(_.toInt))
+    ).map { case Array(Array(sX, sY), Array(bX, bY)) =>
+      ((sX, sY), (bX, bY))
+    }.toMap
+
+  type Point = (Int, Int)
+
+  extension (point: Point)
+    def x = point._1
+    def y = point._2
+
+    def manhattanDistance(to: Point): Int = (x - to.x).abs + (y - to.y).abs
+
+  val beacons = input.values.toList
+
+  val sensorsWithDistance = input.map { case ((sX, sY), (bX, bY)) =>
+    ((sX, sY), (sX, sY).manhattanDistance(bX, bY))
+  }.toMap
+
+  val xMin = sensorsWithDistance.map { case ((x, _), distance) => x - distance }.min
+  val xMax = sensorsWithDistance.map { case ((x, _), distance) => x + distance }.max
+  val yMin = sensorsWithDistance.map { case ((_, y), distance) => y - distance }.min
+  val yMax = sensorsWithDistance.map { case ((_, y), distance) => y + distance }.max
+
+  val part1 = (for x <- xMin to xMax yield (x, 2000000))
+    .filterNot(beacons.contains)
+    .filter(point =>
+      sensorsWithDistance.exists { case (sensor, distance) =>
+        point.manhattanDistance(sensor) <= distance
+      }
+    ).length
+
+  println("Part 1:")
+  println(part1)
+
+  val part2Bound = 4000000
+
+  val posiblePosition = LazyList.iterate((0, 0))(point =>
+    if point.x >= part2Bound then (0, point.y + 1)
+    else
+      sensorsWithDistance
+        .find { case (sensor, distance) =>
+          point.manhattanDistance(sensor) <= distance
+        }.map { case (sensor, distance) =>
+          (
+            point.x + (sensor.x - point.x) + (distance + 1) - ((sensor.y - point.y).abs),
+            point.y
+          )
+        }.getOrElse((point.x + 1, point.y))
+  )
+
+  val beaconPosition = posiblePosition
+    .filter(point => point.x < part2Bound && point.y < part2Bound)
+    .filterNot(point =>
+      sensorsWithDistance.exists { case (sensor, distance) =>
+        point.manhattanDistance(sensor) <= distance
+      }
+    )
+    .head
+
+  val part2 = beaconPosition.x * 4000000L + beaconPosition.y
+  println("Part 2:")
+  println(part2)
+end Day15