Solution 2018-01 (Chronal Calibration)

Author: rhaendel

src/main/kotlin/de/ronny_h/aoc/year2018/day01/ChronalCalibration.kt

@@ -0,0 +1,25 @@
+package de.ronny_h.aoc.year2018.day01
+
+import de.ronny_h.aoc.AdventOfCode
+
+fun main() = ChronalCalibration().run(500, 709)
+
+class ChronalCalibration : AdventOfCode<Int>(2018, 1) {
+    override fun part1(input: List<String>): Int = input.toListOfInt().sum()
+
+    private fun List<String>.toListOfInt(): List<Int> = map {
+        if (it.startsWith('+')) it.substring(1).toInt() else it.toInt()
+    }
+
+    override fun part2(input: List<String>): Int {
+        var frequency = 0
+        val seenFrequencies = mutableSetOf(frequency)
+        generateSequence { input.toListOfInt() }
+            .flatten()
+            .takeWhile {
+                frequency += it
+                seenFrequencies.add(frequency)
+            }.last()
+        return frequency
+    }
+}

src/test/kotlin/de/ronny_h/aoc/year2018/day01/ChronalCalibrationTest.kt

@@ -0,0 +1,23 @@
+package de.ronny_h.aoc.year2018.day01
+
+import de.ronny_h.aoc.extensions.asList
+import io.kotest.core.spec.style.StringSpec
+import io.kotest.matchers.shouldBe
+
+class ChronalCalibrationTest : StringSpec({
+
+    val input = """
+        +1
+        -2
+        +3
+        +1
+    """.asList()
+
+    "part 1: the resulting frequency after all of the changes in frequency have been applied" {
+        ChronalCalibration().part1(input) shouldBe 3
+    }
+
+    "part 2: the first frequency the device reaches twice" {
+        ChronalCalibration().part2(input) shouldBe 2
+    }
+})