Task 1

[summerofcode2018soln.git] / src / task1 / task1.hs

diff --git a/src/task1/task1.hs b/src/task1/task1.hs
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+import Data.List (foldl')        -- import the strict fold
+
+-- number of steps
+type Step = Int
+type Position = (Int, Int)
+
+data Direction = North | East | South | West 
+    deriving (Enum, Show, Bounded, Eq)
+
+-- direction, easting, northing
+data Mowmaster = Mowmaster { direction :: Direction 
+                           , position :: Position
+                           } deriving (Show, Eq)
+
+data Instruction =   Forward Step
+                   | Clockwise 
+                   | Anticlockwise
+                   | Comment String
+    deriving (Show, Eq)
+
+
+
+main :: IO ()
+main = do 
+        instruction_text <- readFile "data/01-mowmaster.txt"
+        print $ part1 instruction_text
+        print $ part2 instruction_text
+
+part1 :: String -> Int
+part1 = length . filter (not . isComment) . lines
+
+part2 :: String -> Int
+part2 instruction_text = finalDistance $ executeAll instructions
+    where instructions = readInstructions instruction_text
+          executeAll = foldl' execute initialMowmaster
+          
+
+
+-- Is this line a comment?
+isComment :: String -> Bool
+isComment ('#':_) = True
+isComment _       = False
+
+
+-- Extract the steps from the input string.
+readInstructions :: String -> [Instruction]
+readInstructions = (map readInstruction) . lines
+
+readInstruction :: String -> Instruction
+readInstruction i = readInstruction' (head i) (tail i)
+    where readInstruction' 'F' s = Forward (read s)
+          readInstruction' 'C' _ = Clockwise
+          readInstruction' 'A' _ = Anticlockwise
+          readInstruction'  _  t = Comment t
+
+
+initialMowmaster = Mowmaster North (0, 0)
+
+
+-- Calculate manhattan distance from start to this state
+finalDistance :: Mowmaster -> Int
+finalDistance m = (abs e) + (abs n)
+    where (e, n) = position m
+
+
+-- Make one move
+execute :: Mowmaster -> Instruction -> Mowmaster
+execute m (Forward s)    = m {position  = forward s (direction m) (position m)}
+execute m  Clockwise     = m {direction = turnCW (direction m)}
+execute m  Anticlockwise = m {direction = turnACW (direction m)}
+execute m (Comment _)    = m
+
+-- Move in the current direction
+forward :: Int -> Direction -> Position -> Position
+forward s North (e, n) = (e, n+s)
+forward s South (e, n) = (e, n-s)
+forward s West  (e, n) = (e-s, n)
+forward s East  (e, n) = (e+s, n)
+
+
+-- | a `succ` that wraps 
+turnCW :: (Bounded a, Enum a, Eq a) => a -> a 
+turnCW dir | dir == maxBound = minBound
+           | otherwise       = succ dir
+
+-- | a `pred` that wraps
+turnACW :: (Bounded a, Enum a, Eq a) => a -> a
+turnACW dir | dir == minBound = maxBound
+            | otherwise       = pred dir