Ex5.hs

module Ex5 where

import Data.List

solve :: String -> Int
solve seatlines = solve2 (lines seatlines)

solve2 :: [String] -> Int
solve2 seats = findSeat (sort (map seatId seats)) (-1)

findSeat :: [Int] -> Int -> Int
findSeat [] x = x
findSeat (s:ss) prev
  | prev + 2 == s = prev + 1
  | otherwise = findSeat ss s

solve1 :: [String] -> Int
solve1 seats = foldr max 0 (map seatId seats)

seatId :: String -> Int
seatId seat = 8*row + column
  where row = index (take 7 seat)
        column = index (drop 7 seat)

index :: String -> Int
index chars = sum (zipWith (\x y -> (topHalf x)*2^y) chars (reverse [0..length chars-1]))

topHalf :: Char -> Int
topHalf 'B' = 1
topHalf 'R' = 1
topHalf 'F' = 0
topHalf 'L' = 0
topHalf c = error ("the char:"++[c]++": caused the problem.")