aoc-2020-day2.hs

p1.hs

module Main where

input =
  [
    -- Use vim `s/...` to make input look like this
    (9, 10, 'm', "mmmmnxmmmwm"),
    -- ...
  ]

isValidPassword (min, max, needle, hay) =
  let
    occurs = length $ filter (== needle) hay
  in
    min <= occurs && occurs <= max

main = print $ length $ filter isValidPassword input

p2.hs

module Main where

import Data.Bits (xor)

input =
  [
    -- Use vim `s/...` to make input look like this
    (9, 10, 'm', "mmmmnxmmmwm"),
    -- ...
  ]

isValidPassword (a, b, needle, hay) =
  needleAt1 a `xor` needleAt1 b

  where
    needleAt1 = (==) needle . (hay !!) . subtract 1

main = print $ length $ filter isValidPassword input