Day 13

Day13.hs

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+module Day13 where
+import System.IO (openFile)
+import Data.Text (unpack, splitOn, pack)
+import Prelude hiding (splitAt)
+import Data.Char (digitToInt)
+import Data.List (nub)
+
+splitAt :: String -> String -> [String]
+splitAt delimiter str = map unpack $ splitOn (pack delimiter) $ pack str
+
+fold :: (Int, Int) -> String -> (Int, Int)
+fold (x, y) str
+    | head str == 'x' = (fold' x, y)
+    | head str == 'y' = (x, fold' y)
+    where coord = read . last $ splitAt "=" str
+          fold' num
+            | num > coord = coord - (num - coord)
+            | otherwise = num
+
+main :: IO ()
+main = do
+    input <- readFile "inputs/13.txt"
+
+    let (coords', folds') = (\[a,b] -> (lines a, lines b)) $ splitAt "\n\n" input
+    --
+    let coords = (\[a,b] -> (read a, read b) :: (Int, Int)) <$> map (splitAt ",") coords'
+        folds  = map (last . splitAt " ") folds'
+
+    print . length . nub $ [fold pos (head folds) | pos <- coords ]

Day13_1.hs

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+module Day13_1 where
+import System.IO (openFile)
+import Data.Text (unpack, splitOn, pack)
+import Prelude hiding (splitAt)
+import Data.Char (digitToInt)
+import Data.List (nub)
+
+splitAt :: String -> String -> [String]
+splitAt delimiter str = map unpack $ splitOn (pack delimiter) $ pack str
+
+insert :: Int -> Char -> [Char] -> [Char]
+insert 0 y xs = xs
+insert n y [] = []
+insert n y xs
+    | length xs < n = xs
+    | otherwise = take n xs ++ [y] ++ insert n y (drop n xs)
+
+
+fold :: String -> (Int, Int) -> (Int, Int)
+fold str (x, y)
+    | head str == 'x' = (fold' x, y)
+    | head str == 'y' = (x, fold' y)
+    where coord = read . last $ splitAt "=" str
+          fold' num
+            | num > coord = coord - (num - coord)
+            | otherwise = num
+
+main :: IO ()
+main = do
+    input <- readFile "inputs/13.txt"
+
+    let (coords', folds') = (\[a,b] -> (lines a, lines b)) $ splitAt "\n\n" input
+    --
+    let coords = (\[a,b] -> (read a, read b) :: (Int, Int)) <$> map (splitAt ",") coords'
+        folds  = map (last . splitAt " ") folds'
+
+    let result = nub $ foldl (\acc x -> map (fold x) acc) coords folds
+
+    let width  = maximum $ fst <$> result
+        height = maximum $ snd <$> result
+        field  = (,) <$> [0..width] <*> [0..height]
+
+    let display x
+            | x `elem` result = '#'
+            | otherwise = '.'
+        -- the text is actually vertical, because of course it is
+        in putStrLn $ insert (height+1) '\n' $ map display field