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Solution 2017-21 (Fractal Art)
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‎src/main/kotlin/de/ronny_h/aoc/year2017/day21/FractalArt.kt‎

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package de.ronny_h.aoc.year2017.day21
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import de.ronny_h.aoc.AdventOfCode
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import de.ronny_h.aoc.extensions.asList
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import de.ronny_h.aoc.extensions.grids.Coordinates
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import de.ronny_h.aoc.extensions.grids.Grid
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fun main() = FractalArt().run(150, 2606275)
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class FractalArt : AdventOfCode<Int>(2017, 21) {
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override fun part1(input: List<String>): Int = applyTheRulesToTheGivenInitConfiguration(input, 5)
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override fun part2(input: List<String>): Int = applyTheRulesToTheGivenInitConfiguration(input, 18)
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fun applyTheRulesToTheGivenInitConfiguration(input: List<String>, iterations: Int): Int {
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val rules = input.parseEnhancementRules()
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val initConfiguration = """
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.#.
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..#
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###
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""".asList()
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var grid = FractalArtGrid(initConfiguration)
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repeat(iterations) {
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grid = grid.applyRules(rules)
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}
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return grid.countPixelsThatAreOn()
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}
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}
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data class Rule(val pattern: List<String>, val onCount: Int, val replacement: List<String>)
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data class RuleSet(val even: List<Rule>, val odd: List<Rule>)
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private const val on = '#'
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private const val off = '.'
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fun List<String>.parseEnhancementRules(): RuleSet {
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val rules = map { input ->
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val (p, r) = input.split(" => ")
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Rule(pattern = p.split("/"), onCount = p.count { it == on }, replacement = r.split("/"))
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}.partition { it.pattern.size % 2 == 0 }
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return RuleSet(even = rules.first, odd = rules.second)
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}
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class FractalArtGrid(size: Int) : Grid<Char>(size, size, off) {
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constructor(initConfiguration: List<String>) : this(initConfiguration.size) {
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check(initConfiguration.size == initConfiguration[0].length) { "FractalArtGrid has to be square" }
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initGrid(initConfiguration)
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}
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override fun Char.toElementType(): Char = this
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fun countPixelsThatAreOn(): Int = forEachElement { _, _, e -> e }.filter { it == on }.count()
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fun applyRules(rules: RuleSet): FractalArtGrid {
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val squareSize = if (height % 2 == 0) 2 else 3
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val numberOfSquares = height / squareSize
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val newGrid = FractalArtGrid(numberOfSquares * (squareSize + 1))
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val rulesToApply = if (height % 2 == 0) rules.even else rules.odd
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forEachSquareOfSize(squareSize) { start, square ->
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var applied = false
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for (rule in rulesToApply) {
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if (rule.onCount != square.countPixelsThatAreOn()) {
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// filter out bad candidates early
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continue
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}
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if (squareSize == 2 && rule.onCount != 2 || rule.ruleMatches(square) || rule.ruleMatches(square.reversed())) {
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newGrid.applyRuleAt(
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rule,
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Coordinates(start.row + (start.row / squareSize), start.col + (start.col / squareSize))
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)
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applied = true
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break
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}
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}
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if (!applied) {
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throw RuntimeException("No rule to apply for square $square at $start.")
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}
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}
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return newGrid
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}
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private fun Rule.ruleMatches(square: List<List<Char>>): Boolean =
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// exact match
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square.allMatch { row, col, value -> pattern[row][col] == value } ||
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// rotate 90° right
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// 0 1
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// 0 [ 0 , 1 ] -> [ 2 , 0 ] = [ 1,0 , 0,0 ] = [ size-col,row , size-col,row ]
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// 1 [ 2 , 3 ] [ 3 , 1 ] [ 1,1 , 0,1 ] [ size-col,row , size-col,row ]
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square.allMatch { row, col, value -> pattern[square.lastIndex - col][row] == value } ||
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// rotate 180°
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// 0 1
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// 0 [ 0 , 1 ] -> [ 3 , 2 ] = [ 1,1 , 1,0 ] = [ size-row,size-col , size-row,size-col ]
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// 1 [ 2 , 3 ] [ 1 , 0 ] [ 0,1 , 0,0 ] [ size-row,size-col , size-row,size-col ]
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square.allMatch { row, col, value -> pattern[square.lastIndex - row][square.lastIndex - col] == value } ||
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// rotate 90° left
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// 0 1
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// 0 [ 0 , 1 ] -> [ 1 , 3 ] = [ 0,1 , 1,1 ] = [ col,size-row , col,size-row ]
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// 1 [ 2 , 3 ] [ 0 , 2 ] [ 0,0 , 1,0 ] [ col,size-row , col,size-row ]
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square.allMatch { row, col, value -> pattern[col][square.lastIndex - row] == value }
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private fun List<List<Char>>.allMatch(condition: (Int, Int, Char) -> Boolean): Boolean {
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forEachIndexed { row, rowList ->
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rowList.forEachIndexed { col, value ->
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if (!condition(row, col, value)) {
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return false
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}
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}
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}
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return true
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}
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private fun applyRuleAt(rule: Rule, start: Coordinates) {
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rule.replacement.forEachIndexed { row, rowString ->
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rowString.forEachIndexed { col, value ->
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this[start.row + row, start.col + col] = value
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}
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}
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}
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private fun forEachSquareOfSize(size: Int, block: (Coordinates, List<List<Char>>) -> Unit) {
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for (row in 0..<height step size) {
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for (col in 0..<height step size) {
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block(Coordinates(row, col), subGridAt(row, col, size))
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}
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}
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}
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}
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private fun List<List<Char>>.countPixelsThatAreOn() = sumOf { row ->
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row.count { it == on }
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}

‎src/test/kotlin/de/ronny_h/aoc/year2017/day21/FractalArtTest.kt‎

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package de.ronny_h.aoc.year2017.day21
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import de.ronny_h.aoc.extensions.asList
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import io.kotest.core.spec.style.StringSpec
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import io.kotest.matchers.shouldBe
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class FractalArtTest : StringSpec({
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val input = """
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../.# => ##./#../...
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.#./..#/### => #..#/..../..../#..#
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""".asList()
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"input can be parsed" {
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input.parseEnhancementRules() shouldBe RuleSet(
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listOf(
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Rule(
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pattern = listOf("..", ".#"),
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onCount = 1,
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replacement = listOf("##.", "#..", "...")
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)
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),
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listOf(
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Rule(
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pattern = listOf(".#.", "..#", "###"),
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onCount = 5,
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replacement = listOf("#..#", "....", "....", "#..#")
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)
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),
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)
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}
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"a 3x3 rule applies to a 3x3 grid that exactly matches the pattern" {
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val rules = listOf(".#./..#/### => #..#/..../..../#..#").parseEnhancementRules()
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val initConfiguration = """
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.#.
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..#
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###
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""".asList()
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val grid = FractalArtGrid(initConfiguration)
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grid.applyRules(rules).toString().trimIndent() shouldBe """
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#..#
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....
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....
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#..#
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""".trimIndent()
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}
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"a 3x3 rule applies to a 3x3 grid that matches the rotated pattern" {
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val rules = listOf(".#./..#/### => #..#/..../..../#..#").parseEnhancementRules()
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val initConfiguration = """
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.##
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#.#
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..#
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""".asList()
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val grid = FractalArtGrid(initConfiguration)
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grid.applyRules(rules).toString().trimIndent() shouldBe """
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#..#
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....
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....
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#..#
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""".trimIndent()
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}
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"a 3x3 rule applies to a 3x3 grid that matches the rotated and flipped pattern" {
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val rules = listOf(".#./..#/### => #..#/..../..../#..#").parseEnhancementRules()
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val initConfiguration = """
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..#
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#.#
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.##
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""".asList()
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val grid = FractalArtGrid(initConfiguration)
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grid.applyRules(rules).toString().trimIndent() shouldBe """
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#..#
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....
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....
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#..#
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""".trimIndent()
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}
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"a 3x3 rule applies to a 3x3 grid that matches the pattern flipped horizontally" {
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val rules = listOf(".#./..#/### => #..#/..../..../#..#").parseEnhancementRules()
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val initConfiguration = """
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.#.
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#..
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###
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""".asList()
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val grid = FractalArtGrid(initConfiguration)
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grid.applyRules(rules).toString().trimIndent() shouldBe """
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#..#
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....
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....
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#..#
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""".trimIndent()
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}
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"a 3x3 rule applies to a 3x3 grid that matches the pattern flipped vertically" {
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val rules = listOf(".#./..#/### => #..#/..../..../#..#").parseEnhancementRules()
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val initConfiguration = """
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###
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..#
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.#.
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""".asList()
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val grid = FractalArtGrid(initConfiguration)
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grid.applyRules(rules).toString().trimIndent() shouldBe """
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#..#
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....
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....
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#..#
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""".trimIndent()
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}
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"a 2x2 rule applies to a 4x4 grid for exact matches of the pattern" {
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val rules = listOf("../.# => ##./#../...").parseEnhancementRules()
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val initConfiguration = """
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....
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.#.#
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....
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.#.#
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""".asList()
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val grid = FractalArtGrid(initConfiguration)
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grid.applyRules(rules).toString().trimIndent() shouldBe """
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##.##.
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#..#..
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......
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##.##.
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#..#..
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......
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""".trimIndent()
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}
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"a 2x2 rule applies to a 4x4 grid for rotated matches of the pattern" {
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val rules = listOf("#./.# => ##./#../...").parseEnhancementRules()
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val initConfiguration = """
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#..#
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.##.
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.##.
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#..#
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""".asList()
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val grid = FractalArtGrid(initConfiguration)
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grid.applyRules(rules).toString().trimIndent() shouldBe """
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##.##.
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#..#..
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......
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##.##.
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#..#..
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......
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""".trimIndent()
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}
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"part 1 and 2: with the example rules, after 2 iterations 12 pixels are on" {
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FractalArt().applyTheRulesToTheGivenInitConfiguration(input, 2) shouldBe 12
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}
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})

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