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Diffstat (limited to '2020/07a.hs')
| -rw-r--r-- | 2020/07a.hs | 36 |
1 files changed, 36 insertions, 0 deletions
diff --git a/2020/07a.hs b/2020/07a.hs new file mode 100644 index 0000000..32c4aaf --- /dev/null +++ b/2020/07a.hs @@ -0,0 +1,36 @@ +module Day7A where + +import System.Environment (getArgs) +import Text.Regex.PCRE + +type Rule = (String, [(Int, String)]) + +parseRule :: String -> Rule +parseRule xs = (parent, children) + where parentMatch = xs =~ "^([a-z ]*) bag" :: [[String]] + parent = head parentMatch!!1 + childrenMatch = xs =~ "([0-9]+) ([a-z ]*) bag" :: [[String]] + childrenNs = map (read . (!! 1)) childrenMatch + childrenNames = map (!! 2) childrenMatch + children = zip childrenNs childrenNames + +-- Keep applying f to a until the output stops changing +untilUnchanged :: Eq a => (a -> a) -> a -> a +untilUnchanged f a | n /= a = untilUnchanged f n + | otherwise = n + where n = f a + +-- Add the bags that can contain these bags to the list +addParents :: [Rule] -> [String] -> [String] +addParents rs xs = map fst $ filter (\(n, cs) -> n `elem` xs || any (`elem` map snd cs) xs) rs + +-- Usage: runghc --ghc-arg="-package regex-pcre-builtin" 7a.hs inputs/day7 +main :: IO () +main = do + args <- getArgs; + content <- readFile $ head args; + let rules = map parseRule $ lines content; + let topLevels = untilUnchanged (addParents rules) ["shiny gold"] + print topLevels; + print $ length topLevels - 1; + return ();
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