commit 15b9d4b793ca200db92fa49cd0aabb33d5a498e6
Author: toast <toby@prufrock.co.uk>
Date:   Thu Dec 4 02:43:18 2025 +0000

    initialise repo; add days 1-3

diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..b4a0e67
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1,2 @@
+**/input.txt
+**/input2.txt
diff --git a/01/solution.hs b/01/solution.hs
new file mode 100644
index 0000000..34f9fb6
--- /dev/null
+++ b/01/solution.hs
@@ -0,0 +1,56 @@
+import Debug.Trace
+import Data.Maybe
+
+traceOut :: Show a => a -> a
+traceOut x = traceShow x x
+
+data Shift = Shift Int
+
+instance Show Shift where
+    show (Shift x) = show x
+
+addFirst :: [[a]] -> a -> [[a]]
+addFirst [] x = [[x]]
+addFirst (y:ys) x = ([x] ++ y) : ys
+
+split :: [Char] -> [Char] -> [[Char]]
+split _ [] = []
+split delims (x:xs)
+  | elem x delims = [[]] ++ split delims xs
+  | otherwise     = addFirst (split delims xs) x
+
+iterateFrom :: [a -> a] -> a -> [a]
+iterateFrom [] x = [x]
+iterateFrom (f:fs) x = x : (iterateFrom fs (f x))
+
+iterateWith :: (a -> b -> b) -> [a] -> b -> [b]
+iterateWith f [] b = [b]
+iterateWith f (a:as) b = b : iterateWith f as (f a b)
+
+parseShift :: String -> Maybe Shift
+parseShift ('L':xs) = Just $ Shift (-(read xs))
+parseShift ('R':xs) = Just $ Shift (read xs)
+parseShift _ = Nothing
+
+parseFile :: String -> Maybe [Shift]
+parseFile = sequence . map parseShift . split ['\n']
+
+toFunc :: Shift -> (Int -> Int)
+toFunc (Shift x) = (+x)
+
+solve1 :: [Shift] -> Int
+solve1 shifts = length $ filter (==0) $ map (`mod` 100) $ iterateFrom (map toFunc shifts) 50
+
+expandShift :: Shift -> [Shift]
+expandShift (Shift x) = take (abs x) $ repeat (Shift (signum x))
+
+solve2 :: [Shift] -> Int
+solve2 = solve1 . foldl (++) [] . map expandShift
+
+main = do 
+    fileinp <- readFile "input.txt"
+    let shifts = fromJust $ parseFile fileinp
+    let solved1 = solve1 shifts
+    let solved2 = solve2 shifts
+    print solved1
+    print solved2
diff --git a/02/solution.hs b/02/solution.hs
new file mode 100644
index 0000000..78d3eb2
--- /dev/null
+++ b/02/solution.hs
@@ -0,0 +1,55 @@
+import Debug.Trace
+
+traceOut :: Show a => a -> a
+traceOut x = traceShow x x
+
+addFirst :: [[a]] -> a -> [[a]]
+addFirst [] x = [[x]]
+addFirst (y:ys) x = ([x] ++ y) : ys
+
+split :: Eq a => [a] -> [a] -> [[a]]
+split _ [] = []
+split delims (x:xs)
+  | elem x delims = [[]] ++ split delims xs
+  | otherwise     = addFirst (split delims xs) x
+
+
+parseFile :: String -> [(Int, Int)]
+parseFile = map ((\(x,y) -> (read x, read (drop 1 y))) . break (=='-')) . split [',']
+
+factors :: Int -> [Int]
+factors 1 = []
+factors 2 = [1]
+factors 3 = [1]
+factors 4 = [1,2]
+factors 5 = [1]
+factors 6 = [1,2,3]
+factors 7 = [1]
+factors 8 = [1,2,4]
+factors 9 = [1,3]
+factors 10 = [1,2,5]
+factors 11 = [1]
+factors 12 = [1,2,3,4,6]
+
+isRepeatN :: Int -> Int -> Bool
+isRepeatN n x = (pow10 x > 0) && ((x `mod` divisor) == 0) && (x `div` divisor < 10^n)
+    where pow10 = (`div` n) . digits
+          divisor = sum $ take (pow10 x) $ iterate (* 10^n) 1
+
+digits = (+1) . floor . logBase 10 . fromInteger . toInteger
+isRepeat2 x = ((digits x) `mod` 2 == 0) && (isRepeatN ((digits x) `div` 2) x)
+isRepeat x = foldl (||) False $ map (`isRepeatN` x) (factors $ digits x)
+
+solve1 :: [(Int, Int)] -> Int
+solve1 = sum . map (sum) . map (filter isRepeat2) . map (\(a, b) -> [a..b])
+
+solve2 :: [(Int, Int)] -> Int
+solve2 = sum . map (sum) . map (filter isRepeat) . map (\(a, b) -> [a..b])
+
+main = do 
+    fileinp <- readFile "input.txt"
+    let input = parseFile fileinp
+    let solved1 = solve1 input
+    let solved2 = solve2 input
+    print solved1
+    print solved2
diff --git a/03/solution.hs b/03/solution.hs
new file mode 100644
index 0000000..e50750e
--- /dev/null
+++ b/03/solution.hs
@@ -0,0 +1,57 @@
+import Debug.Trace
+import Data.Maybe
+import Control.Applicative
+
+instance (Applicative m, Num a) => Num (m a) where
+  (+) = liftA2 (+)
+  (-) = liftA2 (-)
+  (*) = liftA2 (*)
+  abs = fmap abs
+  signum = fmap signum
+  negate = fmap negate
+  fromInteger = pure . fromInteger
+
+traceOut :: Show a => a -> a
+traceOut x = traceShow x x
+
+addFirst :: [[a]] -> a -> [[a]]
+addFirst [] x = [[x]]
+addFirst (y:ys) x = ([x] ++ y) : ys
+
+split :: Eq a => [a] -> [a] -> [[a]]
+split _ [] = []
+split delims (x:xs)
+  | elem x delims = [[]] ++ split delims xs
+  | otherwise     = addFirst (split delims xs) x
+
+parseFile :: String -> [[Int]]
+parseFile = map (map (read . (:[]))) . split ['\n']
+
+dropLast :: Int -> [a] -> [a]
+dropLast n = reverse . drop n . reverse
+
+takeAfter :: (a -> Bool) -> [a] -> [a]
+takeAfter f [] = []
+takeAfter f (x:xs) = if f x then xs else takeAfter f xs
+
+listMax :: Ord a => [a] -> Maybe a
+listMax [] = Nothing
+listMax (x:xs) = Just $ foldl max x xs
+
+bestJoltage :: Int -> [Int] -> Maybe Int
+bestJoltage n xs
+  | n <= 0               = 0
+  | null (drop (n-1) xs) = 0
+  | otherwise            = case maximum of Nothing -> Nothing; Just maximum' -> 10^(n-1) * maximum + (bestJoltage (n-1) (takeAfter (>= maximum') xs))
+        where maximum = listMax $ dropLast (n-1) xs
+
+solve :: Int -> [[Int]] -> Maybe Int
+solve n = fmap sum . sequence . map (bestJoltage n)
+
+main = do 
+    fileinp <- readFile "input.txt"
+    let input = parseFile fileinp
+    let solved1 = fromJust $ solve 2 input
+    let solved2 = fromJust $ solve 12 input
+    print solved1
+    print solved2