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Day 3: Rucksack Reorganization

by @bishabosha

Puzzle description​

https://adventofcode.com/2022/day/3

Final Code​

def part1(input: String): Int =
  val intersections =
    for line <- input.linesIterator yield
      val (left, right) = line.splitAt(line.length / 2)
      (priorities(left) & priorities(right)).head
  intersections.sum

def part2(input: String): Int =
  val badges =
    for case Seq(a, b, c) <- input.linesIterator.grouped(3) yield
      (priorities(a) & priorities(b) & priorities(c)).head
  badges.sum

def priorities(str: String) = str.foldLeft(Priorities.emptySet)(_ add _)

object Priorities:
  opaque type Set = Long // can fit all 52 priorities in a bitset

  // encode priorities as a random access lookup
  private val lookup =
    val arr = new Array[Int](128) // max key is `'z'.toInt == 122`
    for (c, i) <- (('a' to 'z') ++ ('A' to 'Z')).zipWithIndex do
      arr(c.toInt) = i + 1
    IArray.unsafeFromArray(arr)

  val emptySet: Set = 0L

  extension (priorities: Set)
    infix def add(c: Char): Set = priorities | (1L << lookup(c.toInt))
    infix def &(that: Set): Set = priorities & that
    def head: Int = java.lang.Long.numberOfTrailingZeros(priorities)

end Priorities

Run it in the browser​

Part 1​

Part 2​

Solutions from the community​

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