--- /dev/null
+import Text.Parsec hiding (State)
+import Text.ParserCombinators.Parsec.Number
+import Control.Applicative ((<$), (<*), (*>), (<*>), liftA)
+import Data.List (foldl')
+
+data Interval = Interval Int Int deriving (Show, Eq)
+
+low :: Interval -> Int
+low (Interval l _) = l
+
+high :: Interval -> Int
+high (Interval _ h) = h
+
+-- input = 5
+input = 3012210
+
+main :: IO ()
+main = do
+ text <- readFile "advent20.txt"
+ let intervals = successfulParse $ parseIfile text
+ part1 intervals
+ -- part2
+
+part1 :: [Interval] -> IO ()
+part1 intervals = print $ (+1) $ high $ head $ foldl' (mergeAdjacent) [] $ foldl' (merge) [] intervals
+
+part2 :: [Interval] -> IO ()
+part2 intervals = do
+ let ints = foldl' (mergeAdjacent) [] $ foldl' (merge) [] intervals
+ let gapCount = gaps ints
+ let lowGap = max [0, ((low $ head ints) -1)]
+ let highGap = 4294967295 - (min [4294967295, ((high $ last ints) + 1)])
+ print (lowGap + gapCount + highGap)
+
+-- 4294967295
+
+
+disjoint :: Interval -> Interval -> Bool
+disjoint (Interval a b) (Interval c d)
+ | b < c = True
+ | d < a = True
+ | a > d = True
+ | c > b = True
+ | otherwise = False
+
+intersect :: Interval -> Interval -> Bool
+intersect a b = not $ disjoint a b
+
+merge :: [Interval] -> Interval -> [Interval]
+merge [] i0 = [i0]
+merge (i1:intervals) i0
+ | (high i0) < (low i1) = i0:i1:intervals
+ | intersect i0 i1 = merge intervals (Interval a' b')
+ | otherwise = i1:(merge intervals i0)
+ where a' = minimum [low i0, low i1]
+ b' = maximum [high i0, high i1]
+
+mergeAdjacent :: [Interval] -> Interval -> [Interval]
+mergeAdjacent [] i0 = [i0]
+mergeAdjacent (i1:intervals) i0
+ | high i0 + 1 == low i1 = (Interval (low i0) (high i1)):intervals
+ | low i0 == high i1 + 1 = (Interval (low i1) (high i0)):intervals
+ | otherwise = i1:(mergeAdjacent intervals i0)
+
+
+gaps :: [Interval] -> Int
+gaps [] = 0
+gaps [_] = 0
+gaps ((Interval _ b):(Interval c d):intervals) =
+ (c - b - 1) + gaps ((Interval c d):intervals)
+
+
+intervalFile = intervalLine `endBy` newline
+-- IntervalLine = choice [cpyL, incL, decL, jnzL]
+intervalLine = Interval <$> int <*> (string "-" *> int)
+
+
+parseIfile :: String -> Either ParseError [Interval]
+parseIfile input = parse intervalFile "(unknown)" input
+
+parseIline :: String -> Either ParseError Interval
+parseIline input = parse intervalLine "(unknown)" input
+
+successfulParse :: Either ParseError [a] -> [a]
+successfulParse (Left _) = []
+successfulParse (Right a) = a
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