Day 2 ⭐⭐

README.md

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 |              |               |               |           |               |           |               |           |               |           |
 |-------------:|:-------------:|--------------:|:---------:|--------------:|:---------:|--------------:|:---------:|--------------:|:---------:|
 | **[1][d01]** | **[⭐⭐][s01]** |  **[6][d06]** | [☆☆][s06] | **[11][d11]** | [☆☆][s11] | **[16][d16]** | [☆☆][s16] | **[22][d22]** | [☆☆][s22] |
-| **[2][d02]** | **[☆☆][s02]** |  **[7][d07]** | [☆☆][s07] | **[12][d12]** | [☆☆][s12] | **[17][d17]** | [☆☆][s17] | **[23][d23]** | [☆☆][s23] |
+| **[2][d02]** | **[⭐⭐][s02]** |  **[7][d07]** | [☆☆][s07] | **[12][d12]** | [☆☆][s12] | **[17][d17]** | [☆☆][s17] | **[23][d23]** | [☆☆][s23] |
 | **[3][d03]** | **[☆☆][s03]** |  **[8][d08]** | [☆☆][s08] | **[13][d13]** | [☆☆][s13] | **[18][d18]** | [☆☆][s18] | **[24][d24]** | [☆☆][s24] |
 | **[4][d04]** | **[☆☆][s04]** |  **[9][d09]** | [☆☆][s09] | **[14][d14]** | [☆☆][s14] | **[19][d19]** | [☆☆][s19] | **[25][d25]** | [☆☆][s25] |
 | **[5][d05]** | **[☆☆][s05]** | **[10][d10]** | [☆☆][s10] | **[15][d15]** | [☆☆][s15] | **[20][d20]** | [☆☆][s20] |               |           |

src/main/kotlin/Day02.kt

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+import Day02.Color.blue
+import Day02.Color.green
+import Day02.Color.red
+
+class Day02(private val input: List<String>) {
+
+    @Suppress("EnumEntryName")
+    enum class Color { red, green, blue }
+
+    private val regex = """(\d+) (${Color.entries.joinToString("|")})""".toRegex()
+
+    fun part1(
+        target: Map<Color, Int> = mapOf(red to 12, green to 13, blue to 14),
+    ): Int = input.withIndex().filter { (_, line) ->
+        line.split(";")
+            .map { it.cubes() }
+            .all { it.validate(target) }
+    }.sumOf { it.index + 1 }
+
+    fun part2() = input.withIndex().sumOf { (_, line) ->
+        val cubes = line.split(";").map { it.cubes() }
+        fun maxOf(color: Color) = cubes.maxOf { it.getValue(color) }
+        maxOf(red) * maxOf(green) * maxOf(blue)
+    }
+
+    private fun String.cubes(): Map<Color, Int> = regex.findAll(this)
+        .map { it.destructured.let { (amount, color) -> Color.valueOf(color) to amount.toInt() } }
+        .foldInPlace(mutableMapOf<Color, Int>().withDefault { 0 }) { (color, amount) -> merge(color, amount, Int::plus) }
+
+    private fun Map<Color, Int>.validate(target: Map<Color, Int>) = target.all { (key, value) -> getValue(key) <= value }
+
+}

src/main/kotlin/Utils.kt

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+inline fun <T, R> Sequence<T>.foldInPlace(
+    initial: R,
+    operation: R.(T) -> Unit,
+): R = fold(initial) { acc: R, t: T -> acc.apply { operation(t) } }
+

src/test/kotlin/Day02Test.kt

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+import Day02.Color.blue
+import Day02.Color.green
+import Day02.Color.red
+import Resources.readLines
+import org.junit.jupiter.api.DisplayName
+import org.junit.jupiter.api.Nested
+import org.junit.jupiter.api.Test
+import kotlin.test.assertEquals
+
+@DisplayName("Day 02")
+class Day02Test {
+
+    private val sampleInput = readLines("Day02-sample.txt")
+    private val actualInput = readLines("Day02.txt")
+
+    @Nested
+    @DisplayName("Part 1")
+    inner class Part1 {
+
+        @Test
+        fun `Matches example`() {
+            assertEquals(
+                expected = 8,
+                actual = Day02(sampleInput).part1(),
+            )
+        }
+
+        @Test
+        fun `Actual answer`() = assertEquals(
+          expected = 2169,
+          actual = Day02(actualInput).part1(),
+        )
+
+    }
+
+    @Nested
+    @DisplayName("Part 2")
+    inner class Part2 {
+
+        @Test
+        fun `Matches example`() = assertEquals(
+            expected = 2286,
+            actual = Day02(sampleInput).part2(),
+        )
+
+        @Test
+        fun `Actual answer`() = assertEquals(
+            expected = 60948,
+            actual = Day02(actualInput).part2(),
+        )
+
+    }
+
+}

src/test/resources/Day02-sample.txt

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+Game 1: 3 blue, 4 red; 1 red, 2 green, 6 blue; 2 green
+Game 2: 1 blue, 2 green; 3 green, 4 blue, 1 red; 1 green, 1 blue
+Game 3: 8 green, 6 blue, 20 red; 5 blue, 4 red, 13 green; 5 green, 1 red
+Game 4: 1 green, 3 red, 6 blue; 3 green, 6 red; 3 green, 15 blue, 14 red
+Game 5: 6 red, 1 blue, 3 green; 2 blue, 1 red, 2 green