Day 17

input/2021/day17-sample1.txt

@@ -0,0 +1 @@
+target area: x=20..30, y=-10..-5

input/2021/day17-sample2.txt

@@ -0,0 +1 @@
+target area: x=179..201, y=-109..-63

input/2021/day17.txt

@@ -0,0 +1 @@
+target area: x=143..177, y=-106..-71

src/main/scala/de.qwertyuiop.aoc/2021/day17.scala

@@ -1,6 +1,62 @@
 package de.qwertyuiop.aoc.`2021`
 
-import de.qwertyuiop.aoc.lib.*
+import de.qwertyuiop.aoc.lib.{*, given}
+import Vectors.*
 import cats.*, cats.implicits.given
+import ProbeStatus.*
 
-def day17(using InputSource): Unit = ???
+def day17(using InputSource): Unit =
+  given Ordering[Vec2D[Int]] = (summon[Ordering[(Int,Int)]].asInstanceOf[Ordering[Vec2D[Int]]])
+  val s"target area: x=${xMinS}..${xMaxS}, y=${yMinS}..${yMaxS}" = input().head
+  val (xMin, xMax, yMin, yMax)  = (xMinS.toInt, xMaxS.toInt, yMinS.toInt, yMaxS.toInt)
+  val xRange = xMin to xMax
+  val yRange = yMin to yMax
+  val zero = Vec2D(0,0)
+
+  def simulateSteps(pos: Vec2D[Int], xVelocity: Int, yVelocity: Int, visited: List[Vec2D[Int]]): List[Vec2D[Int]] =
+    if pos.x > xMax || pos.y < yMin then pos :: visited
+    else if xVelocity == 0 && !xRange.contains(pos.x) then pos:: visited
+    else
+      simulateSteps(
+        pos + Vec2D(xVelocity, yVelocity),
+        if xVelocity == 0 then 0 else xVelocity- xVelocity.sign,
+        yVelocity - 1,
+        pos :: visited
+      )
+
+  def minXSpeedRec(start: Int, sum: Int): Int =
+    if sum < xMin then minXSpeedRec(start + 1, sum + start)
+    else start -2
+  val minXSpeed = minXSpeedRec(0,0)
+
+  def checkSolution(steps: List[Vec2D[Int]]): ProbeStatus =
+    val overshot :: candidate :: _ = steps
+    if xRange.contains(candidate.x) && yRange.contains(candidate.y) then Hit
+    else if overshot.x < xMin then TooNear
+    else TooFar
+
+  case class Flight(xSpeed: Int, ySpeed: Int, highest: Int)
+  def highestY(xSpeed: Int) =
+    val hits = LazyList.range(yMin, yMin + 1000).map(ySpeed => {
+                val sim = simulateSteps(zero, xSpeed, ySpeed, List())
+                (xSpeed, ySpeed, sim, checkSolution(sim))
+              }).dropWhile(_._4 != Hit).take(1000).filter(_._4 == Hit)
+    hits.map{ case (x,y,t,_) => Flight(x, y, y * (y + 1) / 2) }
+
+  val flights = (
+    for
+      xSpeed <- minXSpeed to xMax + 10
+      flight <- highestY(xSpeed).toList
+    yield flight
+  )
+  val Flight(dxMax, dyMax, top) = flights.maxBy(_._3)
+  println(s"Top height: $top")
+  println(s"Number of valid shots: ${flights.size}")
+
+
+
+
+enum ProbeStatus:
+  case Hit
+  case TooNear
+  case TooFar

src/main/scala/de.qwertyuiop.aoc/lib/vectors.scala

@@ -89,7 +89,6 @@ object Vectors:
   given [T: Monoid]: Monoid[Vec3D[T]] = semiauto.monoid
   given [T: Monoid]: Monoid[Vec4D[T]] = semiauto.monoid
 
-
   given [T: Numeric]: Vec[Vec3D[T]] with
     extension (v: Vec3D[T])
       def +(w: Vec3D[T]): Vec3D[T] = (v._1 + w._1, v._2 + w._2, v._3 + w._3)