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1 files changed, 66 insertions, 0 deletions

diff --git a/2021/day10/10b.hs b/2021/day10/10b.hs
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+module Main where
+
+import Data.List (sort)
+
+isStartParen :: Char -> Bool
+isStartParen '(' = True
+isStartParen '[' = True
+isStartParen '{' = True
+isStartParen '<' = True
+isStartParen _ = False
+
+isEndParen :: Char -> Bool
+isEndParen ')' = True
+isEndParen ']' = True
+isEndParen '}' = True
+isEndParen '>' = True
+isEndParen _ = False
+
+flipParen :: Char -> Char
+flipParen '(' = ')'
+flipParen ')' = '('
+flipParen '[' = ']'
+flipParen ']' = '['
+flipParen '{' = '}'
+flipParen '}' = '{'
+flipParen '<' = '>'
+flipParen '>' = '<'
+flipParen _ = undefined
+
+getScore :: Char -> Int
+getScore ')' = 3
+getScore ']' = 57
+getScore '}' = 1197
+getScore '>' = 25137
+
+completionScore :: Char -> Int
+completionScore ')' = 1
+completionScore ']' = 2
+completionScore '}' = 3
+completionScore '>' = 4
+completionScore _ = undefined
+
+consumeBlock :: Char -> String -> Either Char String
+consumeBlock t "" = Right ""
+consumeBlock t (c:cs) | c == flipParen t  = Right cs
+                      | isStartParen c    = (consumeBlock c cs) >>= (consumeBlock t)
+                      | otherwise         = Left c
+
+corruptionScore :: String -> Int
+corruptionScore "" = 0
+corruptionScore (c:cs) = case consumeBlock c cs of
+                      Left c -> getScore c
+                      Right s -> corruptionScore s
+
+getCompletion :: String -> String -> String
+getCompletion stack "" = map flipParen stack
+getCompletion stack (c:cs) | isStartParen c = getCompletion (c : stack) cs
+                           | otherwise      = getCompletion (tail stack) cs
+
+main :: IO ()
+main = do
+  s <- readFile "./input"
+  let notCorrupted = filter ((== 0) . corruptionScore) (lines s)
+  let scores = sort $ map ((foldl (\acc x -> (acc * 5) + (completionScore x)) 0) . getCompletion "") notCorrupted
+
+  print $ scores !! (div (length scores) 2)