Day 2

[advent-of-code-18.git] / src / advent02 / advent02.hs

diff --git a/src/advent02/advent02.hs b/src/advent02/advent02.hs
new file mode 100644 (file)
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+++ b/src/advent02/advent02.hs
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+import Data.List
+
+
+main :: IO ()
+main = do 
+        text <- readFile "data/advent02.txt"
+        let ids = lines text
+        print $ part1 ids
+        putStrLn $ part2 ids
+
+part1 ids = (fst counts23) * (snd counts23)
+    where allLetterCounts = map letterCounts ids
+          counts23 = foldl' addCounts (0, 0) allLetterCounts
+
+letterCounts :: String -> [Int]
+letterCounts = map length . group . sort
+
+addCounts :: (Int, Int) -> [Int] -> (Int, Int)
+addCounts (twos, threes) counts = (twos', threes')
+    where twos'   = if has2 counts then twos + 1   else twos
+          threes' = if has3 counts then threes + 1 else threes
+
+has2 = elem 2
+has3 = elem 3
+
+part2 ids = uncurry sameChars closeIds
+    where closeIds = head $ filter (\ab -> uncurry differenceCount ab == 1) [(a, b) | a <- ids, b <- ids]
+
+differenceCount :: String -> String -> Int
+differenceCount this that = length $ filter (\(a, b) -> a /= b) $ zip this that
+
+sameChars :: String -> String -> String
+sameChars this that = map fst $ filter (\(a, b) -> a == b) $ zip this that
+