aoc2023/Day9.scala
2023-12-09 13:23:52 +01:00

39 lines
831 B
Scala

package aoc.day9
import aoc._
object Parser extends CommonParser:
val nums = rep1(long)
val lns = lines.toSeq
val inputs = lns.map(Parser.parse(Parser.nums, _).get).toSeq
// part1
def calculate(add: Int => (Long, Seq[Long]) => Long)(ns: Seq[Long]) =
@scala.annotation.tailrec
def loop(ns: Seq[Long], depth: Int, sum: Long): Long =
if ns.forall(_ == 0) then sum
else
val diff = ns.tail.lazyZip(ns).map(_ - _)
loop(diff, depth + 1, add(depth)(sum, ns))
loop(ns, 0, 0)
def part1 =
println(inputs.map(calculate(_ => (sum, ns) => sum + ns.last)).sum)
// part 2
def part2 =
println(
inputs
.map(
calculate(depth => (sum, ns) => sum + ns.head * (if depth % 2 == 0 then 1 else -1))
)
.sum
)
@main def Day9(part: Int) = part match
case 1 => part1
case 2 => part2