Day 5

[advent-of-code-18.git] / src / advent05 / advent05.hs

diff --git a/src/advent05/advent05.hs b/src/advent05/advent05.hs
new file mode 100644 (file)
index 0000000..4aa6746
--- /dev/null
+++ b/src/advent05/advent05.hs
@@ -0,0 +1,53 @@
+import Data.List
+import Data.Char (toLower)
+
+main :: IO ()
+main = do 
+        text <- readFile "data/advent05.txt"
+        -- let ids = lines text
+        print $ part1 text
+        print $ part2 text
+        -- putStrLn $ part2 ids
+
+
+part1 = reactedLength
+
+part2 polymer = minimum finalLengths
+    where finalLengths = map (\u -> reactedLength $ removeUnit polymer u) units
+          units = unitsPresent polymer
+
+
+react :: String -> Char -> Char -> String -> (String, String)
+react prefix a b suffix = 
+    if willReact a b
+    then (prefix, suffix)
+    else ((b:a:prefix), suffix)
+
+willReact :: Char -> Char -> Bool
+willReact a b = (a /= b) && (toLower a == toLower b)
+
+
+reactHere :: (String, String) -> Maybe ((String, String), (String, String))
+reactHere (prefix, suffix) = 
+    if canContinue prefix suffix
+    then Just ((prefix'', suffix''), (prefix'', suffix''))
+    else Nothing
+    where (prefix', a, b, suffix') = reactionSite prefix suffix
+          (prefix'', suffix'') = react prefix' a b suffix'
+
+
+canContinue (_:_) (_:_) = True
+canContinue [] (_:_:_) = True
+canContinue _ _ = False
+
+reactionSite (a:prefix) (b:suffix) = (prefix, a, b, suffix)
+reactionSite [] (a:b:suffix) = ([], a, b, suffix)
+
+
+reactedLength polymer = length prefix + length suffix
+    where (prefix, suffix) = last $ unfoldr reactHere ("", polymer)
+
+
+unitsPresent = nub . sort . map toLower 
+
+removeUnit polymer unit = filter (\c -> toLower c /= unit ) polymer