Aoc2021-day7.scala

package lascala.aoc2021.day1_10.day7

def findMinCost(from: Int, to: Int, cost: Int => Int): Int =
  val mid      = (from + to) / 2
  val fromCost = cost(from)
  val toCost   = cost(to)

  if (from + 1) >= to then (fromCost min toCost)
  else if fromCost >= toCost then findMinCost(mid, to, cost)
  else findMinCost(from, mid, cost)

def flatFuel(xs: IndexedSeq[Int])(x: Int): Int =
  xs.map(_ - x).map(_.abs).sum

def incrementalFuel(xs: IndexedSeq[Int])(x: Int): Int =
  xs.map(_ - x).map(_.abs).map(x => x * (x + 1) / 2).sum

def solve1(s: String): BigInt =
  val xs = s.split(",").map(_.toInt).toIndexedSeq
  findMinCost(xs.min, xs.max, flatFuel(xs))
end solve1

def solve2(s: String): BigInt =
  val xs = s.split(",").map(_.toInt).toIndexedSeq
  findMinCost(xs.min, xs.max, incrementalFuel(xs))
end solve2

@main def part1: Unit =
  val ans = solve1(input)
  println(ans)

@main def part2: Unit =
  val ans = solve2(input)
  println(ans)

val input =

Aoc2021-day7Test.scala

package lascala.aoc2021.day1_10.day7

import minitest.SimpleTestSuite
import hedgehog.minitest.HedgehogSupport
import hedgehog.*

object Day7Test extends SimpleTestSuite with HedgehogSupport:

  val testInput = """16,1,2,0,4,2,7,1,2,14"""

  example("day7 - solve1") {
    solve1(testInput) ==== 37
  }

  example("day7 - solve2") {
    solve2(testInput) ==== 168
  }

end Day7Test