Day 2 part 1 + beginning of part 2

2024/.idea/vcs.xml

@@ -2,6 +2,6 @@
 <project version="4">
   <component name="VcsDirectoryMappings">
     <mapping directory="" vcs="Git" />
-    <mapping directory="$PROJECT_DIR$" vcs="Git" />
+    <mapping directory="$PROJECT_DIR$/.." vcs="Git" />
   </component>
 </project>

2024/src/main/kotlin/Utils.kt

@@ -0,0 +1,4 @@
+fun readInput(name: String) = object {}.javaClass.getResourceAsStream(name)
+    ?.bufferedReader()
+    ?.lineSequence()
+    ?: error("Cannot read input")

2024/src/main/kotlin/day1.kt

@@ -1,10 +1,7 @@
 import kotlin.math.abs
 
 fun main() {
-    val input = object {}.javaClass.getResourceAsStream("day1.txt")
-        ?.bufferedReader()
-        ?.lineSequence()
-        ?: error("Cannot read input")
+    val input = readInput("day1.txt")
 
     val a = mutableListOf<Int>()
     val b = mutableListOf<Int>()

2024/src/main/kotlin/day2.kt

@@ -0,0 +1,33 @@
+import kotlin.math.abs
+
+fun main() {
+    val input = readInput("day2.txt")
+        .map { line -> line.split(" ").map { it.toInt() } }
+
+    val safe = input.count { isSafe(it) }
+    println("Part 1: $safe")
+}
+
+private fun isSafe(report: List<Int>): Boolean {
+    data class State(val increasing: Boolean? = null, val last: Int? = null, val safe: Boolean = true, val usedProblemDampener: Boolean = false) {
+        fun update(next: Int): State = when {
+            !safe -> this
+            last == null -> copy(last = next)
+            increasing == null -> copy(increasing = last < next, last = next, safe = safeIncrement(last, next))
+            increasing -> copy(last = next, safe = safeIncrement(last, next) && last < next)
+            else -> copy(last = next, safe = safeIncrement(last, next) && last > next)
+        }.problemDampener()
+
+        fun safeIncrement(last: Int, next: Int): Boolean = abs(last - next) in 1..3
+
+        fun problemDampener() = when {
+            !safe && !usedProblemDampener -> copy(safe = true, usedProblemDampener = true)
+            else -> this
+        }
+    }
+
+    return report.fold(State()) { state, next ->
+        state.update(next)
+            .also { if (!it.safe) return@fold it }
+    }.safe
+}