Day 3

src/day03.scala

@@ -0,0 +1,72 @@
+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)))
+
+final case class Coord(x: Int, y: Int)
+final case class PartNumber(number: Int, coord: Coord, length: Int):
+  def isAdjacentTo(aCoord: Coord) =
+    coord.x - 1 <= aCoord.x && coord.x + length >= aCoord.x &&
+      coord.y - 1 <= aCoord.y && coord.y + 1 >= aCoord.y
+
+def parseLine(line: String, y: Int): List[PartNumber] =
+  @tailrec def aux(startsAt: Int, acc: List[PartNumber]): List[PartNumber] =
+    if startsAt >= line.length - 1 then acc
+    else if line(startsAt).isDigit then
+      val number = parseNumber(startsAt, line, y)
+      aux(startsAt + number.length, number :: acc)
+    else aux(startsAt + 1, acc)
+  aux(0, List())
+
+def findCoords(lines: Array[String], filter: Char => Boolean) =
+  for
+    x <- (0 to lines(0).length - 1)
+    y <- (0 to lines.length - 1)
+    if (filter(lines(y)(x)))
+  yield Coord(x, y)
+
+def parseNumber(startsAt: Int, line: String, y: Int): PartNumber =
+  val digits = line.drop(startsAt).takeWhile(_.isDigit)
+  PartNumber(digits.toInt, Coord(startsAt, y), length = digits.length)
+
+def part1(input: String): String =
+
+  val lines = input.split("\n")
+
+  def isSymbol(char: Char) = !(char.isDigit || char == '.')
+  val symbolsCoords = findCoords(lines, isSymbol)
+
+  lines.zipWithIndex
+    .flatMap(parseLine)
+    .filter(p => symbolsCoords.exists(p.isAdjacentTo(_)))
+    .map(_.number)
+    .sum
+    .toString
+
+def part2(input: String): String =
+
+  def isGearSymbol(char: Char) = char == '*'
+
+  val lines = input.split("\n")
+
+  val gearsCoords = findCoords(lines, isGearSymbol)
+
+  val parts =
+    lines.zipWithIndex
+      .flatMap(parseLine)
+
+  gearsCoords
+    .map(g => parts.filter(_.isAdjacentTo(g)))
+    .collect {
+      case parts if parts.length == 2 => parts.map(_.number).product
+    }
+    .sum
+    .toString