Solve 2024 day 15 part 2

sim642 · Dec 15, 2024 · 4dd8a4f · 4dd8a4f
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diff --git a/src/main/scala/eu/sim642/adventofcode2024/Day15.scala b/src/main/scala/eu/sim642/adventofcode2024/Day15.scala
@@ -15,30 +15,100 @@ object Day15 {
 
   case class Input(grid: Grid[Char], moves: Seq[Pos])
 
-  def simulateMove(grid: Grid[Char], robot: Pos, move: Pos): (Grid[Char], Pos) = {
-    val newRobot = robot + move
-    val newBox = Iterator.iterate(newRobot)(_ + move).find(grid(_) != 'O').get
-    if (grid(newBox) == '.')
-      (grid.updatedGrid(newBox, 'O').updatedGrid(newRobot, '.'), newRobot)
-    else
-      (grid, robot)
+  trait Part {
+    def simulateMove(grid: Grid[Char], robot: Pos, move: Pos): (Grid[Char], Pos)
+    def sumBoxGps(grid: Grid[Char]): Int
+
+    def sumMovesBoxGps(input: Input): Int = {
+      val initialRobot = input.grid.posOf('@')
+      val initialGrid = input.grid.updatedGrid(initialRobot, '.')
+      val (finalGrid, finalRobot) = input.moves.foldLeft((initialGrid, initialRobot))({ case ((grid, robot), move) =>
+        simulateMove(grid, robot, move)
+      })
+      sumBoxGps(finalGrid)
+    }
   }
 
-  def sumBoxGps(grid: Grid[Char]): Int = {
-    (for {
-      (row, y) <- grid.view.zipWithIndex
-      (cell, x) <- row.view.zipWithIndex
-      if cell == 'O'
-    } yield 100 * y + x).sum
+  object Part1 extends Part {
+    override def simulateMove(grid: Grid[Char], robot: Pos, move: Pos): (Grid[Char], Pos) = {
+      val newRobot = robot + move
+      val newBox = Iterator.iterate(newRobot)(_ + move).find(grid(_) != 'O').get
+      if (grid(newBox) == '.')
+        (grid.updatedGrid(newBox, 'O').updatedGrid(newRobot, '.'), newRobot)
+      else
+        (grid, robot)
+    }
+
+    override def sumBoxGps(grid: Grid[Char]): Int = {
+      (for {
+        (row, y) <- grid.view.zipWithIndex
+        (cell, x) <- row.view.zipWithIndex
+        if cell == 'O'
+      } yield 100 * y + x).sum
+    }
   }
 
-  def sumMovesBoxGps(input: Input): Int = {
-    val initialRobot = input.grid.posOf('@')
-    val initialGrid = input.grid.updatedGrid(initialRobot, '.')
-    val (finalGrid, finalRobot) = input.moves.foldLeft((initialGrid, initialRobot))({ case ((grid, robot), move) =>
-      simulateMove(grid, robot, move)
-    })
-    sumBoxGps(finalGrid)
+  object Part2 extends Part {
+    def scaleGrid(grid: Grid[Char]): Grid[Char] = {
+      grid.map(_.flatMap({
+        case '#' => "##"
+        case 'O' => "[]"
+        case '.' => ".."
+        case '@' => "@."
+      }))
+    }
+
+    override def simulateMove(grid: Grid[Char], robot: Pos, move: Pos): (Grid[Char], Pos) = {
+
+      def helper(grid: Grid[Char], pos: Pos): Option[Grid[Char]] = grid(pos) match {
+        case '.' => Some(grid)
+        case '#' => None
+        case '[' if move.x == 0 => // vertical
+          for {
+            newGrid <- helper(grid, pos + move)
+            newGrid2 <- helper(newGrid, pos + Pos(1, 0) + move)
+          } yield newGrid2.updatedGrid(pos + move, '[').updatedGrid(pos + Pos(1, 0) + move, ']').updatedGrid(pos, '.').updatedGrid(pos + Pos(1, 0), '.')
+        case ']' if move.x == 0 => // vertical
+          for {
+            newGrid <- helper(grid, pos + move)
+            newGrid2 <- helper(newGrid, pos - Pos(1, 0) + move)
+          } yield newGrid2.updatedGrid(pos + move, ']').updatedGrid(pos - Pos(1, 0) + move, '[').updatedGrid(pos, '.').updatedGrid(pos - Pos(1, 0), '.')
+        case '[' if move.y == 0 => // horizontal
+          for {
+            newGrid <- helper(grid, pos + move)
+          } yield newGrid.updatedGrid(pos + move, '[').updatedGrid(pos, '.')
+        case ']' if move.y == 0 => // horizontal
+          for {
+            newGrid <- helper(grid, pos + move)
+          } yield newGrid.updatedGrid(pos + move, ']').updatedGrid(pos, '.')
+        case _ => ???
+      }
+
+      val newRobot = robot + move
+      helper(grid, newRobot) match {
+        case Some(newGrid) => (newGrid, newRobot)
+        case None => (grid, robot)
+      }
+    }
+
+    override def sumBoxGps(grid: Grid[Char]): Int = {
+      printGrid(grid)
+      (for {
+        (row, y) <- grid.view.zipWithIndex
+        (cell, x) <- row.view.zipWithIndex
+        if cell == '['
+        //gpsX = x min (row.size - 1 - x)
+        //gpsY = y min (grid.size - 1 - y)
+        gpsX = x
+        gpsY = y
+        () = println((gpsX, gpsY))
+      } yield 100 * gpsY + gpsX).sum
+    }
+
+    override def sumMovesBoxGps(input: Input): Int = {
+      val scaledGrid = scaleGrid(input.grid)
+      super.sumMovesBoxGps(Input(scaledGrid, input.moves))
+    }
   }
 
   def parseGrid(s: String): Grid[Char] = s.linesIterator.map(_.toVector).toVector
@@ -49,9 +119,18 @@ object Day15 {
     case s"$grid\n\n$moves" => Input(parseGrid(grid), parseMoves(moves))
   }
 
+  def printGrid(grid: Grid[Char]): Unit = {
+    for (row <- grid) {
+      for (cell <- row)
+        print(cell)
+      println()
+    }
+  }
+
   lazy val input: String = scala.io.Source.fromInputStream(getClass.getResourceAsStream("day15.txt")).mkString.trim
 
   def main(args: Array[String]): Unit = {
-    println(sumMovesBoxGps(parseInput(input)))
+    println(Part1.sumMovesBoxGps(parseInput(input)))
+    println(Part2.sumMovesBoxGps(parseInput(input)))
   }
 }
diff --git a/src/test/scala/eu/sim642/adventofcode2024/Day15Test.scala b/src/test/scala/eu/sim642/adventofcode2024/Day15Test.scala
@@ -40,12 +40,33 @@ class Day15Test extends AnyFunSuite {
       |
       |<^^>>>vv<v>>v<<""".stripMargin
 
+  val exampleInput3 =
+    """#######
+      |#...#.#
+      |#.....#
+      |#..OO@#
+      |#..O..#
+      |#.....#
+      |#######
+      |
+      |<vv<<^^<<^^""".stripMargin
+
   test("Part 1 examples") {
-    assert(sumMovesBoxGps(parseInput(exampleInput2)) == 2028)
-    assert(sumMovesBoxGps(parseInput(exampleInput)) == 10092)
+    assert(Part1.sumMovesBoxGps(parseInput(exampleInput2)) == 2028)
+    assert(Part1.sumMovesBoxGps(parseInput(exampleInput)) == 10092)
   }
 
   test("Part 1 input answer") {
-    assert(sumMovesBoxGps(parseInput(input)) == 1476771)
+    assert(Part1.sumMovesBoxGps(parseInput(input)) == 1476771)
+  }
+
+  test("Part 2 examples") {
+    assert(Part2.sumMovesBoxGps(parseInput(exampleInput3)) == 618) // from glguy
+    assert(Part2.sumMovesBoxGps(parseInput(exampleInput2)) == 1751) // from glguy
+    assert(Part2.sumMovesBoxGps(parseInput(exampleInput)) == 9021)
+  }
+
+  test("Part 2 input answer") {
+    assert(Part2.sumMovesBoxGps(parseInput(input)) == 1468005)
   }
 }