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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
ruleFor :: String -> [Rule] -> Rule
-- ruleFor x rs | null r = (x, [])
-- | otherwise = head r
-- where r = filter ((== x) . fst) rs
ruleFor x = head . filter ((== x) . fst)
nBags :: [Rule] -> String -> Int
nBags rs x = 1 + sum [n * nBags rs c | (n, c) <- snd $ ruleFor x 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;
print $ nBags rules "shiny gold" - 1;
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