advent09/src/advent09.hs

   1 -- import Debug.Trace
   2
   3 import Data.List
   4
   5 main :: IO ()
   6 main =
   7     do  numStrs <- readFile "data/advent09.txt"
   8         let nums = map (read @Int) $ lines numStrs
   9         let firstInvalid = part1 nums
  10         print firstInvalid
  11         print $ part2 firstInvalid nums
  12
  13 part1 nums = fst $ head $ filter (not . valid) $ slidingWindow 25 nums
  14
  15 slidingWindow winSize nums =
  16     zip (drop winSize nums) $ map (take winSize) $ tails nums
  17
  18 valid (target, window) = not $ null [(x, y) | x <- window, y <- window, x + y == target]
  19
  20
  21 part2 target nums = (maximum section) + (minimum section)
  22     where section = head $ filter (sumsToTarget target) $ subStrings smallNums
  23           smallNums = dropWhileEnd (>= target) nums
  24
  25 -- subStrings :: [a] -> [[a]]
  26 subStrings = (concatMap inits) . tails
  27
  28 -- sumsToTarget :: Int -> [Int] -> Bool
  29 sumsToTarget target ns = sum ns == target
  30