Day 3

src/Day2503.hs

@@ -0,0 +1,49 @@
+module Main where
+
+import Data.List (tails, singleton)
+import Data.Maybe (fromMaybe)
+import Data.Map qualified as M
+
+import Debug.Trace (trace, traceWith)
+
+pairs :: [a] -> [(a,a)]
+pairs l = [(x,y) | (x:ys) <- tails l, y <- ys]
+
+digitCount :: Int -> Int
+digitCount 0 = 0
+digitCount n = 1 + digitCount (n `div` 10)
+
+--------------------
+----- Problems -----
+--------------------
+
+part1 :: String -> Int
+part1 = sum . map (processBank . map (read . singleton)) . lines
+  where
+  processBank :: [Int] -> Int
+  processBank = maximum . map (\(a,b) -> 10*a+b) . pairs
+
+part2 :: String -> Int
+part2 = sum . map (findMax 12 . map (read . singleton)) . lines
+  where
+  findMax :: Int -> [Int] -> Int
+  findMax n xs'       = foldl (\acc curr -> curr + 10 * acc) 0 $ go xs' 0
+    where
+    go :: [Int] -> Int -> [Int]
+    go _ p  | p == n = []
+    go xs p | length xs == n-p = xs
+
+    go xs@(x:rest) p | lookWidth <= 0  = xs
+                     | maxRem == x     = x:go rest (p+1)
+                     | otherwise       =   go rest  p
+      where
+      lookWidth = length xs - (n-p) + 1
+      maxRem = maximum $ take lookWidth xs
+
+main :: IO ()
+main = do
+  str <- getContents
+
+  print $ part1 str
+  print $ part2 str
+