Complete day 6

day6/day6.kt

@@ -0,0 +1,43 @@
+import java.io.File
+import kotlin.text.Regex
+
+fun main() {
+    val input = File("input")
+
+    val races = parseRaces(input)
+    println(part1(races))
+
+    val singleRace = parseSingleRace(input)
+    println(part1(listOf(singleRace)))
+}
+
+fun part1(races: List<Pair<Long, Long>>): Long {
+    return races.map { getNumberOfWins(it.first, it.second) }.reduce { count, acc -> count * acc }
+}
+
+fun getNumberOfWins(time: Long, distance: Long): Long {
+    val wins = (0..time / 2).filter { it * (time - it) > distance }.count()
+
+    return when (time % 2) {
+        0L -> (wins - 1L) * 2L + 1L
+        1L -> wins * 2L
+        else -> throw Exception("Unreachable")
+    }
+}
+
+fun parseSingleRace(input: File): Pair<Long, Long> {
+    return input.useLines {
+        val numbers =
+                it
+                        .map { it.split(':').drop(1).single().filter { it.isDigit() }.toLong() }
+                        .iterator()
+        Pair(numbers.next(), numbers.next())
+    }
+}
+
+fun parseRaces(input: File): List<Pair<Long, Long>> {
+    return input.useLines {
+        val numbers = it.map { it.split(Regex("\\s+")).drop(1).map { it.toLong() } }.iterator()
+        numbers.next().zip(numbers.next()).map { (time, distance) -> Pair(time, distance) }
+    }
+}

day6/input

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+Time:        60     80     86     76
+Distance:   601   1163   1559   1300

day6/test

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+Time:      7  15   30
+Distance:  9  40  200