Day 17 - puzzle 1.

Author: lakiboy

.gitignore

@@ -1,3 +1,4 @@
 .gradle
 .idea
 build
+/bin

src/main/kotlin/io/dmitrijs/aoc2022/Day17.kt

@@ -0,0 +1,138 @@
+package io.dmitrijs.aoc2022
+
+class Day17(input: String) {
+ private val moves = input.trim()
+
+ fun puzzle1(): Int {
+ val board = Board(7)
+ var moveIndex = 0
+
+ repeat(2022) { step ->
+ val figure = figures[step % figures.size].also { board.place(it) }
+
+ do {
+ val leftOrRight = Direction.of(moves[moveIndex])
+ moveIndex = ++moveIndex % moves.length
+ board.move(figure, leftOrRight)
+ } while (board.move(figure, Direction.DOWN))
+
+ board.freeze(figure)
+ }
+
+ return board.figuresHeight
+ }
+
+ private class Board(private val width: Int, private val topBlankLines: Int = 3) {
+ private val field = ArrayDeque<String>()
+ private val blankLine = SPACE.toString().repeat(width)
+ private var position = start
+
+ val figuresHeight get() = field.size
+
+ fun place(figure: Figure) {
+ position = start
+ field.insertBlankLines(topBlankLines + figure.height)
+ }
+
+ fun freeze(figure: Figure) {
+ figure.placeAt(position)
+ field.removeBlankLines()
+ }
+
+ fun move(figure: Figure, direction: Direction): Boolean {
+ val next = position + direction
+
+ return canMove(figure, next).also { success ->
+ if (success) {
+ position = next
+ }
+ }
+ }
+
+ private fun canMove(figure: Figure, position: Point): Boolean {
+ val (posX, posY) = position
+
+ if (posX < 0 || (posX + figure.width) > width || (posY + figure.height) > field.size) {
+ return false
+ }
+
+ return (0 until figure.height).all { y ->
+ (0 until figure.width).all { x ->
+ field[posY + y][posX + x] == SPACE || figure[y][x] == SPACE
+ }
+ }
+ }
+
+ override fun toString() = field.joinToString("\n")
+
+ private fun Figure.placeAt(position: Point) = repeat(height) { y ->
+ val line = field[position.y + y]
+ val replace = this[y].mapIndexed { x, char ->
+ // This is the trick - take char from original line if figure has space.
+ char.takeUnless { it == SPACE } ?: line[position.x + x]
+ }.joinToString("")
+
+ field[position.y + y] = line.substring(0, position.x) + replace + line.substring(position.x + width)
+ }
+
+ private fun ArrayDeque<String>.insertBlankLines(count: Int) = repeat(count) {
+ addFirst(blankLine)
+ }
+
+ private fun ArrayDeque<String>.removeBlankLines() {
+ do {
+ val line = first()
+ if (line == blankLine) {
+ removeFirst()
+ }
+ } while (line == blankLine)
+ }
+ }
+
+ private data class Figure(private val lines: List<String>) {
+ val width = lines.first().length
+ val height = lines.size
+
+ operator fun get(row: Int) = lines[row]
+
+ companion object {
+ fun of(vararg shape: String) = Figure(shape.toList())
+ }
+ }
+
+ private fun Direction.Companion.of(char: Char) = when (char) {
+ '>' -> Direction.RIGHT
+ '<' -> Direction.LEFT
+ else -> error("Invalid direction supplied: $char.")
+ }
+
+ companion object {
+ private const val SPACE = '.'
+ private val start = Point(2, 0)
+ private val figures = listOf(
+ Figure.of(
+ "@@@@",
+ ),
+ Figure.of(
+ ".@.",
+ "@@@",
+ ".@.",
+ ),
+ Figure.of(
+ "..@",
+ "..@",
+ "@@@",
+ ),
+ Figure.of(
+ "@",
+ "@",
+ "@",
+ "@",
+ ),
+ Figure.of(
+ "@@",
+ "@@",
+ ),
+ )
+ }
+}

src/test/kotlin/io/dmitrijs/aoc2022/Day17Test.kt

@@ -0,0 +1,27 @@
+package io.dmitrijs.aoc2022
+
+import io.dmitrijs.aoc2022.Resources.resourceAsText
+import org.junit.jupiter.api.DisplayName
+import org.junit.jupiter.api.Nested
+import kotlin.test.Test
+import kotlin.test.assertEquals
+
+@DisplayName("Day 17")
+internal class Day17Test {
+ private val exampleInput = resourceAsText("day17_example")
+ private val problemInput = resourceAsText("day17")
+
+ @Nested
+ @DisplayName("Puzzle 1")
+ inner class Puzzle1 {
+ @Test
+ fun `solves example`() {
+ assertEquals(3_068, Day17(exampleInput).puzzle1())
+ }
+
+ @Test
+ fun `solves problem`() {
+ assertEquals(3_106, Day17(problemInput).puzzle1())
+ }
+ }
+}

src/test/resources/day17_example.txt

@@ -0,0 +1 @@
+>>><<><>><<<>><>>><<<>>><<<><<<>><>><<>>