Merge pull request #11 from ephemient/kt/day2

README.md

@@ -6,4 +6,4 @@ Development occurs in language-specific directories:
 |[Haskell](hs) ![Haskell CI](https://github.com/ephemient/aoc2024/workflows/Haskell%20CI/badge.svg)|[Kotlin](kt) ![Kotlin CI](https://github.com/ephemient/aoc2024/workflows/Kotlin%20CI/badge.svg)|[Python](py) ![Python CI](https://github.com/ephemient/aoc2024/workflows/Python%20CI/badge.svg)|[Rust](rs) ![Rust CI](https://github.com/ephemient/aoc2024/workflows/Rust%20CI/badge.svg)|
 |--:|--:|--:|--:|
 |[Day1.hs](hs/src/Day1.hs)|[Day1.kt](kt/aoc2024-lib/src/commonMain/kotlin/com/github/ephemient/aoc2024/Day1.kt)|[day1.py](py/aoc2024/day1.py)|[day1.rs](rs/src/day1.rs)|
-|[Day2.hs](hs/src/Day2.hs)||||
+|[Day2.hs](hs/src/Day2.hs)|[Day2.kt](kt/aoc2024-lib/src/commonMain/kotlin/com/github/ephemient/aoc2024/Day2.kt)|||

kt/aoc2024-exe/src/commonBench/kotlin/com/github/ephemient/aoc2024/exe/Day2Bench.kt

@@ -0,0 +1,23 @@
+package com.github.ephemient.aoc2024.exe
+
+import com.github.ephemient.aoc2024.Day2
+import kotlinx.benchmark.Benchmark
+import kotlinx.benchmark.Scope
+import kotlinx.benchmark.Setup
+import kotlinx.benchmark.State
+
+@State(Scope.Benchmark)
+class Day2Bench {
+    private lateinit var input: String
+
+    @Setup
+    fun setup() {
+        input = getDayInput(1)
+    }
+
+    @Benchmark
+    fun part1() = Day2(input).part1()
+
+    @Benchmark
+    fun part2() = Day2(input).part2()
+}

kt/aoc2024-lib/src/commonMain/kotlin/com/github/ephemient/aoc2024/Day2.kt

@@ -0,0 +1,39 @@
+package com.github.ephemient.aoc2024
+
+class Day2(input: String) {
+    private val reports = input.lineSequence().mapNotNull { line ->
+        val words = line.split(splitter)
+        IntArray(words.size) { words[it].toIntOrNull() ?: return@mapNotNull null }
+    }.toList()
+
+    fun part1() = reports.count(::isSafe1)
+
+    fun part2() = reports.count(::isSafe2)
+
+    companion object {
+        private val splitter = """\s+""".toRegex()
+
+        private fun isSafe1(report: IntArray): Boolean {
+            var decreasing = false
+            var increasing = false
+            for (i in 0..report.size - 2) {
+                when (report[i + 1] - report[i]) {
+                    in -3..-1 -> decreasing = true
+                    in 1..3 -> increasing = true
+                    else -> return false
+                }
+            }
+            return !(decreasing && increasing)
+        }
+
+        private fun isSafe2(report: IntArray): Boolean {
+            if (report.isEmpty()) return true
+            val report2 = report.copyOf(report.size - 1)
+            for (i in report2.lastIndex downTo 0) {
+                if (isSafe1(report2)) return true
+                report2[i] = report[i + 1]
+            }
+            return isSafe1(report2)
+        }
+    }
+}

kt/aoc2024-lib/src/commonMain/kotlin/com/github/ephemient/aoc2024/Days.kt

@@ -2,6 +2,7 @@ package com.github.ephemient.aoc2024
 
 val days: List<Day> = listOf(
     Day(1, ::Day1, Day1::part1, Day1::part2),
+    Day(2, ::Day2, Day2::part1, Day2::part2),
 )
 
 data class Day(

kt/aoc2024-lib/src/commonTest/kotlin/com/github/ephemient/aoc2024/Day2Test.kt

@@ -0,0 +1,28 @@
+package com.github.ephemient.aoc2024
+
+import kotlin.test.Test
+import kotlin.test.assertEquals
+
+class Day2Test {
+    @Test
+    fun part1() {
+        assertEquals(2, Day2(example).part1())
+    }
+
+    @Test
+    fun part2() {
+        assertEquals(4, Day2(example).part2())
+    }
+
+    companion object {
+        private val example =
+            """
+            |7 6 4 2 1
+            |1 2 7 8 9
+            |9 7 6 2 1
+            |1 3 2 4 5
+            |8 6 4 4 1
+            |1 3 6 7 9
+            |""".trimMargin()
+    }
+}