2020/13/p1.hs at main · eldridge.cam/advent-of-code

Advent of Code solutions

advent-of-code / 2020 / 13 / p1.hs

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 1import Data.List
 2import Data.Ord
 3
 4split :: Eq a => a -> [a] -> [[a]]
 5split x ys = splitInner x [] ys
 6    where
 7        splitInner _ [] [] = []
 8        splitInner _ r [] = [reverse r]
 9        splitInner x r (y : ys)
10            | x == y = reverse r : splitInner x [] ys
11            | otherwise = splitInner x (y : r) ys
12
13main :: IO ()
14main = do
15    [arrival, buses] <- lines <$> getContents
16    let
17        start = read arrival
18        intervals = [read n | n <- split ',' buses, n /= "x"] :: [Int]
19        waits = [(n, n - start `mod` n) | n <- intervals]
20        in print . uncurry (*) $ minimumBy (comparing snd) waits