Day 6 ⭐⭐

README.md

@@ -2,7 +2,7 @@
 
 |              |               |               |           |               |           |               |           |               |           |
 |-------------:|:-------------:|--------------:|:---------:|--------------:|:---------:|--------------:|:---------:|--------------:|:---------:|
-| **[1][d01]** | **[⭐⭐][s01]** |  **[6][d06]** | [☆☆][s06] | **[11][d11]** | [☆☆][s11] | **[16][d16]** | [☆☆][s16] | **[22][d22]** | [☆☆][s22] |
+| **[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] |
 | **[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] |

src/main/kotlin/Day06.kt

@@ -0,0 +1,21 @@
+class Day06(private val input: List<String>) {
+
+    fun part1(): Long = input
+        .map { """\d+""".toRegex().findAll(it).map(MatchResult::value).map(String::toLong) }
+        .let { (times, distances) -> (times zip distances) }
+        .map { (time, distance) -> wins(time, distance) }
+        .product()
+
+    fun part2(): Long = input
+        .map { it.filter(Char::isDigit).toLong() }
+        .let { (time, distance) -> wins(time, distance) }
+
+    private fun wins(time: Long, distance: Long): Long {
+        var min = 0
+        while (min * (time - min) <= distance) min++
+        var max = time
+        while (max * (time - max) <= distance) max--
+        return (max - min + 1)
+    }
+
+}

src/main/kotlin/Utils.kt

@@ -8,3 +8,8 @@ inline fun <T, R> Sequence<T>.foldIndexedInPlace(
     operation: R.(index: Int, T) -> Unit,
 ): R = foldIndexed(initial) { index: Int, acc: R, t: T -> acc.apply { operation(index, t) } }
 
+@JvmName("intProduct")
+fun Sequence<Int>.product(): Long = fold(1L, Long::times)
+
+@JvmName("longProduct")
+fun Sequence<Long>.product(): Long = fold(1L, Long::times)

src/test/kotlin/Day06Test.kt

@@ -0,0 +1,49 @@
+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 06")
+class Day06Test {
+
+    private val sampleInput = readLines("Day06-sample.txt")
+    private val actualInput = readLines("Day06.txt")
+
+    @Nested
+    @DisplayName("Part 1")
+    inner class Part1 {
+
+        @Test
+        fun `Matches example`() = assertEquals(
+            expected = 288,
+            actual = Day06(sampleInput).part1(),
+        )
+
+        @Test
+        fun `Actual answer`() = assertEquals(
+            expected = 449820,
+            actual = Day06(actualInput).part1(),
+        )
+
+    }
+
+    @Nested
+    @DisplayName("Part 2")
+    inner class Part2 {
+
+        @Test
+        fun `Matches example`() = assertEquals(
+            expected = 71503,
+            actual = Day06(sampleInput).part2(),
+        )
+
+        @Test
+        fun `Actual answer`() = assertEquals(
+            expected = 42250895,
+            actual = Day06(actualInput).part2(),
+        )
+
+    }
+
+}

src/test/resources/Day06-sample.txt

@@ -0,0 +1,2 @@
+Time:      7  15   30
+Distance:  9  40  200