Day Nine 2023

day_nine_2023.hs

{-# LANGUAGE OverloadedStrings #-}
module DayNine where

import qualified Data.Text as T
import qualified Text.Read as TR
import qualified Data.List as L
import Safe (atMay, tailMay)
import qualified Data.Maybe as M
import Lib (operateOnFile)

derivative = L.unfoldr calculateDifference
  where calculateDifference items = do
                                      firstElement <- items `atMay` 0
                                      secondElement <- items `atMay` 1
                                      tail <- tailMay items
                                      return (secondElement - firstElement, tail)

allDerivatives :: [Int] -> [[Int]]
allDerivatives f = takeWhile notDone $ iterate derivative f
  where notDone = any (/= 0)

seeds = (map head) . allDerivatives

integrate seed [] = []
integrate seed derivative@(h:t) = (seed) : (integrate (seed + h) t)

generify f = foldr integrate (repeat 0) (seeds f)

extrapolatedValue f = (generify f) !! (length f)

testInput :: [T.Text]
testInput = ["0 3 6 9 12 15",
    "1 3 6 10 15 21",
    "10 13 16 21 30 45"]

partOne lines = sum $ map extrapolatedValue $ parsed
  where parsed :: [[Int]]
        parsed = map (M.catMaybes . (map readString) . (T.split (== ' '))) lines
        readString = TR.readMaybe . T.unpack

partTwo lines = sum $ map (extrapolatedValue . reverse) $ parsed
  where parsed :: [[Int]]
        parsed = map (M.catMaybes . (map readString) . (T.split (== ' '))) lines
        readString = TR.readMaybe . T.unpack