aoc-2020-day5

p1.hs

module Main where

import Data.List (foldl')

parseBinary = foldl' (\acc v -> acc*2 + (if v then 1 else 0)) 0

seatId = parseBinary . map (`elem` "BR")

main = do
  raw <- readFile "./d5.txt"
  print $ maximum $ map seatId $ words raw

p2.hs

module Main where

import Data.List (foldl', sort)

parseBinary = foldl' (\acc v -> acc*2 + (if v then 1 else 0)) 0

seatId = parseBinary . map (`elem` "BR")

s x y z = x z (y z)

pairwise = s zip tail

-- Original solution was a little less cutesy
mySeatId =
  (+) 1 . fst . head . filter (\(a, b) -> a == b - 2) . pairwise . sort . map seatId

main = do
  raw <- readFile "./d5.txt"
  print $ mySeatId $ words raw