Solution Day 15, part one

Author: rhaendel

src/main/kotlin/Day14.kt

@@ -123,7 +123,7 @@ fun main() {
 
     fun part2(input: List<String>) = iterateUntilSymmetrical(input.parseRobots(), 101, 103)
 
-    printAndCheck(input, ::part2, 91649162)
+    printAndCheck(input, ::part2, 6512)
 }
 
 data class Robot(val px: Int, val py: Int, val vx: Int, val vy: Int)

src/main/kotlin/Day15.kt

@@ -0,0 +1,106 @@
+import de.ronny_h.extensions.Coordinates
+import de.ronny_h.extensions.Direction
+import de.ronny_h.extensions.Grid
+
+fun main() {
+    val day = "Day15"
+
+    println("$day part 1")
+
+    fun part1(input: List<String>): Int {
+        val warehouse = Warehouse(input.takeWhile { it.isNotBlank() })
+        warehouse.printGrid()
+
+        val movements = input
+            .takeLastWhile { it.isNotBlank() }
+            .joinToString(separator = "")
+            .map {
+                when (it) {
+                    '^' -> Direction.NORTH
+                    '>' -> Direction.EAST
+                    'v' -> Direction.SOUTH
+                    '<' -> Direction.WEST
+                    else -> error("Unexpected direction Char: $it")
+                }
+            }
+
+        warehouse.moveRobot(movements)
+        warehouse.printGrid()
+
+        return warehouse.sumGPSCoordinates()
+    }
+
+    printAndCheck(
+        """
+            ########
+            #..O.O.#
+            ##@.O..#
+            #...O..#
+            #.#.O..#
+            #...O..#
+            #......#
+            ########
+            
+            <^^>>>vv<v>>v<<
+        """.trimIndent().lines(),
+        ::part1, 2028
+    )
+
+    val testInput = readInput("${day}_test")
+    printAndCheck(testInput, ::part1, 10092)
+
+    val input = readInput(day)
+    printAndCheck(input, ::part1, 1463715)
+}
+
+private class Warehouse(input: List<String>) : Grid<Char>(input) {
+    private val wall = '#'
+    private val robot = '@'
+    private val free = '.'
+    private val goods = 'O'
+
+    override val nullElement = wall
+    override fun Char.toElementType(): Char = this
+
+    fun moveRobot(movements: List<Direction>) {
+        movements.fold(findTheRobot()) { position, direction ->
+            if (tryToMove(position, direction, robot)) {
+                position + direction
+            } else {
+                position
+            }
+        }
+    }
+
+    private fun tryToMove(from: Coordinates, direction: Direction, thing: Char): Boolean {
+        val target = from + direction
+        if (getAt(target) == free) {
+            setAt(target, thing)
+            setAt(from, free)
+            return true
+        }
+        if (getAt(target) == wall) {
+            return false
+        }
+        check(getAt(target) == goods)
+        if (tryToMove(target, direction, goods)) {
+            setAt(target, thing)
+            setAt(from, free)
+            return true
+        }
+        return false
+    }
+
+    private fun findTheRobot(): Coordinates = forEachElement { row, col, element ->
+        if (element == robot) Coordinates(row, col) else null
+    }.filterNotNull().first()
+
+    fun sumGPSCoordinates(): Int = forEachElement { row, col, element ->
+        if (element == goods) {
+            100 * row + col
+        } else {
+            0
+        }
+    }.sum()
+
+}

src/main/kotlin/de/ronny_h/extensions/Grid.kt

@@ -20,6 +20,9 @@ abstract class Grid<T>(input: List<String>) {
     }
 
     fun getAt(position: Coordinates) = get(position.row, position.col)
+    fun setAt(position: Coordinates, element: T) {
+        grid[position.row][position.col] = element
+    }
 
     fun <R> forEachIndex(action: (row: Int, col: Int) -> R): Sequence<R> = sequence {
         for (row in grid.indices) {

src/test/kotlin/de/ronny_h/extensions/GridTest.kt

@@ -73,6 +73,15 @@ class GridTest : StringSpec() {
             grid[2, 2] shouldBe Int.MIN_VALUE
         }
 
+        "setAt sets the element at the given coordinates" {
+            val grid = simpleCharGridOf(listOf("12", "34"))
+            grid.setAt(Coordinates(1, 0), '5')
+            grid[0, 0] shouldBe '1'
+            grid[0, 1] shouldBe '2'
+            grid[1, 0] shouldBe '5'
+            grid[1, 1] shouldBe '4'
+        }
+
         "forEachIndex calls the provided function on each element in the expected order" {
             val grid = simpleCharGridOf(listOf("12", "34"))
             val chars = grid.forEachIndex { row, column ->