day6

day6.scala

package com.rubenverg.aoc2021

import utils.*

object Day6 extends Day:
  def run(iterations: Int, input: String) =
    // `Int#times` just takes an initial input and then calls the given function that many times
    // that weird `groupBy` and `view` and `mapValue` stuff essentially just takes the list and turns it into a map of item -> count
    iteration.times(input.split(',').map(_.trim.toInt).groupBy(identity).view.mapValues(s => BigInt(s.size)).toMap) { map =>
      Map(
        0 -> map.getOrElse(1, BigInt(0)),
        1 -> map.getOrElse(2, BigInt(0)),
        2 -> map.getOrElse(3, BigInt(0)),
        3 -> map.getOrElse(4, BigInt(0)),
        4 -> map.getOrElse(5, BigInt(0)),
        5 -> map.getOrElse(6, BigInt(0)),
        6 -> (map.getOrElse(7, BigInt(0)) + map.getOrElse(0, BigInt(0))),
        7 -> map.getOrElse(8, BigInt(0)),
        8 -> map.getOrElse(0, BigInt(0))
      )
    }

  def part1(input: String) =
    run(80, input).values.sum
  def part2(input: String) =
    run(256, input).values.sum