add initial day5 solution

1 files changed, 33 insertions, 0 deletions

diff --git a/execs/Day05.hs b/execs/Day05.hs
new file mode 100644
index 0000000..4251cd6
--- /dev/null
+++ b/execs/Day05.hs
@@ -0,0 +1,33 @@
+module Main where
+
+import           Text.ParserCombinators.Parsec
+import Data.List (sort)
+import Control.Monad
+
+data Direction = Upper | Lower
+
+doHalving :: [Direction] -> (Int, Int) -> (Int, Int)
+doHalving [] p = p
+doHalving (Lower:rest) (l, u) = doHalving rest (l, (u+l) `div` 2)
+doHalving (Upper:rest) (l, u) = doHalving rest ((u+l) `div` 2 + 1, u)
+
+findId :: (Int, Int) -> Int
+findId (row, col) = row * 8 + col
+
+doValidate :: String -> Int
+doValidate s = findId (row, col)
+    where row = fst $ flip doHalving (0, 127) $ map readDir (take 7 s)
+          col = fst $ flip doHalving (0, 7) $ map readDir (drop 7 s)
+
+readDir :: Char -> Direction
+readDir c
+  | c `elem` "FL" = Lower
+  | otherwise = Upper
+
+main :: IO ()
+main = do
+    n <- lines <$> readFile "input/05"
+    let valids = map doValidate n
+        ans1 = maximum valids
+    print ans1
+    print $ sum [minimum valids .. ans1] - sum valids