Day 3

src/day03.scala

@@ -0,0 +1,46 @@
+package aoc
+package day03
+
+import scala.annotation.tailrec
+
+val dayNumber = "03"
+
+@main def part1: Unit =
+  println(part1(loadInput(dayNumber)))
+
+@main def part2: Unit =
+  println(part2(loadInput(dayNumber)))
+
+def part1(input: String): String =
+
+  def solve(digits: String) =
+    val highestDigitIdx = digits.dropRight(1).zipWithIndex.maxBy(_._1)._2
+    s"${digits(highestDigitIdx)}${digits.drop(highestDigitIdx + 1).max}".toInt
+
+  input
+    .split('\n')
+    .map(solve)
+    .sum
+    .toString
+
+def part2(input: String): String =
+
+  def solve(digits: String) =
+    @tailrec
+    def rec(digits: String, selected: List[Char], toSelectCount: Int): Long =
+      if toSelectCount == 0 then selected.reverse.mkString.toLong
+      else
+        val highestDigitIdx = digits.dropRight(toSelectCount - 1).zipWithIndex.maxBy(_._1)._2
+        rec(
+          digits.drop(highestDigitIdx + 1),
+          digits(highestDigitIdx) :: selected,
+          toSelectCount - 1
+        )
+
+    rec(digits, List.empty, 12)
+
+  input
+    .split('\n')
+    .map(solve)
+    .sum
+    .toString