Advent of Code, Day 1

In the first day of Advent of Code, the task is to first calculate the fuel needed for some mass, and then treat that fuel as mass, and calculate the fuel needed for that and so on, then add it together.

Nothing special going on in this code, so I’ll just post it:

module Day1 where

fuelForMass :: Integer -> Integer
fuelForMass mass = (mass `div` 3) - 2

fuelForMassRec :: Integer -> Integer
fuelForMassRec mass = go mass 0
  where
    go 0    acc = acc
    go mass acc =
      let
        fuel = fuelForMass mass
      in
        if fuel <= 0
        then acc
        else go fuel (acc + fuel)

part1 :: IO Integer
part1 = do
  input <- readFile "../input/day1.txt"
  let fuel = (fuelForMass . read <$> lines input) :: [Integer]
  return $ foldr (+) 0 fuel

part2 :: IO Integer
part2 = do
  input <- readFile "../input/day1.txt"
  let fuels = (fuelForMassRec . read <$> lines input) :: [Integer]
  return $ foldr (+) 0 fuels