eldridge.cam
Advent of Code solutions
1data Instruction
2 = N Int
3 | E Int
4 | S Int
5 | W Int
6 | R Int
7 | L Int
8 | F Int
9 deriving (Show, Eq)
10
11l :: Pos -> Pos
12l (x, y) = (-y, x)
13
14r :: Pos -> Pos
15r (x, y) = (y, -x)
16
17parse :: String -> Instruction
18parse ('N' : rest) = N (read rest)
19parse ('E' : rest) = E (read rest)
20parse ('S' : rest) = S (read rest)
21parse ('W' : rest) = W (read rest)
22parse ('R' : rest) = R (read rest `div` 90)
23parse ('L' : rest) = L (read rest `div` 90)
24parse ('F' : rest) = F (read rest)
25parse _ = error "Invalid instruction"
26
27type Pos = (Int, Int)
28
29run :: [Instruction] -> (Pos, Pos) -> (Pos, Pos)
30run [] = id
31run (i : is) = run is . apply i
32
33apply :: Instruction -> (Pos, Pos) -> (Pos, Pos)
34apply (N n) ((x, y), p) = ((x, y + n), p)
35apply (S n) ((x, y), p) = ((x, y - n), p)
36apply (E n) ((x, y), p) = ((x + n, y), p)
37apply (W n) ((x, y), p) = ((x - n, y), p)
38apply (L 0) h = h
39apply (L n) (w, p) = apply (L $ n - 1) (l w, p)
40apply (R 0) h = h
41apply (R n) (w, p) = apply (R $ n - 1) (r w, p)
42apply (F n) ((dx, dy), (x, y)) = ((dx, dy), (x + dx * n, y + dy * n))
43
44main :: IO ()
45main = do
46 instructions <- fmap parse . lines <$> getContents
47 let (_, (x, y)) = run instructions ((10, 1), (0, 0)) in
48 print $ abs x + abs y