Solve point of incidence, part 1

Author: ncke

solutions/13_example.txt

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+#.##..##.
+..#.##.#.
+##......#
+##......#
+..#.##.#.
+..##..##.
+#.#.##.#.
+
+#...##..#
+#....#..#
+..##..###
+#####.##.
+#####.##.
+..##..###
+#....#..#

solutions/13_incidence.hs

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+import Data.List
+import System.Environment (getArgs)
+
+type Mirror = ([String], [String])
+
+main = do
+    args <- getArgs
+    input <- readFile (args !! 0)
+    let mirrors = parse (lines input)
+
+    print(answer1 mirrors)
+
+-- Answer 1.
+
+answer1 :: [Mirror] -> Int
+answer1 ms = foldl (+) 0 [contribution (m1, m2) | (m1, m2) <- ms]
+
+contribution (m1, m2) = case (symmetryLine m1, symmetryLine m2) of
+    (Just n, Nothing) -> 100 * (n + 1)
+    (Nothing, Just n) -> (n + 1)
+
+symmetryLine :: [String] -> Maybe Int
+symmetryLine strs = find (isSymmetry strs) [0..(length strs)-2]
+
+isSymmetry :: [String] -> Int -> Bool
+isSymmetry strs n = (take smallest before) == (take smallest after)
+    where
+        before = [strs !! i | i <- reverse [0..n]]
+        after = [strs !! i | i <- [n + 1..(length strs) - 1]]
+        smallest = min (length before) (length after)
+
+-- Answer 2.
+
+
+
+-- Parse input.
+
+parse :: [String] -> [Mirror]
+parse strs = [(n, rotateNote n) | n <- parseNotes [] [] strs]
+
+parseNotes :: [[String]] -> [String] -> [String] -> [[String]]
+parseNotes acc note [] = acc ++ [note]
+parseNotes acc note (s : strs)
+    | null s = parseNotes (acc ++ [note]) [] strs
+    | otherwise = parseNotes acc (note ++ [s]) strs
+
+rotateNote :: [String] -> [String]
+rotateNote strs = [col x | x <- [0..xSz-1]]
+    where
+        (xSz, ySz) = (length (strs !! 0), length strs)
+        at x y = (strs !! y) !! x
+        col x = [ at x y | y <- [0..ySz-1]]