day1: add solution

.gitignore

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+*.in

Day1A.hs

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+module Day1A where
+
+read' :: String -> Integer
+read' ('+':str) = read str
+read' str = read str
+
+main :: IO ()
+main = interact $ show . sum . map read' . lines

Day1B.hs

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+module Day1B where
+
+import Day1A (read')
+import qualified Data.Set as S
+
+handle :: Integer -> (S.Set Integer) -> [Integer] -> Integer
+handle freq history (nextDelta:xs)
+  | S.member freq history = freq  -- When the frequency is in the history set, return it
+  | otherwise             = handle (freq + nextDelta) (S.insert freq history) xs  -- Recurse otherwise
+handle _ _ _ = error "xs should not be empty :("
+
+main :: IO ()
+main = interact $ show . handle 0 S.empty . deltaFreqs
+  where deltaFreqs = cycle . map read' . lines  -- Convert input to Integers and repeat infinitely