Solve Day 2

2024/src/main/kotlin/aoc/year2024/Day2.kt

@@ -0,0 +1,28 @@
+package aoc.year2024
+
+import aoc.library.Puzzle
+import kotlin.math.absoluteValue
+
+object Day2 : Puzzle<Int, Int>(day = 2) {
+
+  override fun solvePart1(input: String): Int = parse(input).count { reportIsSafe(it) }
+
+  override fun solvePart2(input: String): Int = parse(input)
+    .count { report ->
+      report.indices.any { removeIndex ->
+        val adjustedReport = report.toMutableList()
+          .apply { removeAt(removeIndex) }
+        reportIsSafe(adjustedReport)
+      }
+    }
+
+  private fun reportIsSafe(report: List<Int>): Boolean {
+    val steps = report.windowed(2).map { it[1] - it[0] }
+    val monotonic = steps.all { it > 0 } || steps.all { it < 0 }
+    return monotonic && steps.all { it.absoluteValue in 1..3 }
+  }
+
+  private fun parse(input: String): List<List<Int>> = input.lines().map {
+    it.split(" ").map(String::toInt)
+  }
+}

2024/src/test/kotlin/aoc/year2024/Day2Test.kt

@@ -0,0 +1,38 @@
+package aoc.year2024
+
+import aoc.library.solvePart1
+import aoc.library.solvePart2
+import io.kotest.matchers.ints.shouldBeExactly
+import org.junit.jupiter.api.Test
+
+class Day2Test {
+
+  private val testInput = """
+      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
+  """.trimIndent()
+
+  @Test
+  fun part1TestInput() {
+    Day2.solvePart1(testInput) shouldBeExactly 2
+  }
+
+  @Test
+  fun part1() {
+    Day2.solvePart1() shouldBeExactly 341
+  }
+
+  @Test
+  fun part2TestInput() {
+    Day2.solvePart2(testInput) shouldBeExactly 4
+  }
+
+  @Test
+  fun part2() {
+    Day2.solvePart2() shouldBeExactly 404
+  }
+}