dnf: day 12, solve: day 13, part 1

2020/12/Day12.hs

@@ -0,0 +1,95 @@
+module Day12 ( Action
+             , Inst
+             , action
+             , value
+             , Program
+             , parseProgram
+             , State
+             , position
+             , heading
+             , start
+             , run
+             ) where
+
+import Data.Char
+import Text.ParserCombinators.ReadP
+
+data Action = N | S | E | W | L | R | F
+  deriving (Eq, Show)
+
+data Inst = Inst { action :: Action, value :: Int }
+  deriving (Eq, Show)
+
+inst :: ReadP Inst
+inst = do
+  a <- action'
+  v <- int
+  return $ Inst a v
+    where
+      int :: ReadP Int
+      int = do
+        digits <- munch1 isDigit
+        return $ read digits
+      action' :: ReadP Action
+      action' = do
+        a <- choice $ map char "NSEWLRF"
+        return $ case a of
+          'N' -> N
+          'S' -> S
+          'E' -> E
+          'W' -> W
+          'L' -> L
+          'R' -> R
+          'F' -> F
+
+type Program = [Inst]
+
+program :: ReadP Program
+program = inst `sepBy1` skipSpaces
+
+parse p s = parsedResult $ readP_to_S p s
+  where
+    parsedResult [(a, _)] = a
+    parsedResult (a:as)    = parsedResult as
+    parsedResult _         = error "Parser error"
+
+parseProgram = parse program
+
+data State = State { position :: (Int, Int)
+                   , heading :: Action -- This isn't "correct"
+                   } deriving (Eq, Show)
+
+start = State (0, 0) E
+
+updatePosition :: State -> ((Int -> Int), (Int -> Int)) -> State
+updatePosition s (deltaX, deltaY) = State np (heading s)
+  where
+    (x, y) = position s
+    np = (deltaX x, deltaY y)
+
+
+updateHeading :: State -> Action -> State
+updateHeading s nh = State (position s) nh
+
+travel :: State -> Inst -> State
+travel s i = updatePosition s $ case i of
+                                  (Inst N d) -> (id, (+) d)
+                                  (Inst E d) -> ((+) d, id)
+                                  (Inst S d) -> (id, (-) d)
+                                  (Inst W d) -> ((-) d, id)
+
+headings = cycle [N, E, S, W]
+rotate h (Inst d v) = headings !! (v `div` 90)
+  where
+    headings = dropWhile (/= h) $ cycle $ case d of
+                                            R -> [N, E, S, W]
+                                            L -> [N, W, S, E]
+
+tick :: State -> Inst -> State
+tick s i@(Inst a v)
+  | a == N || a == S || a == E || a == W = travel s i
+  | a == L || a == R = updateHeading s $ rotate (heading s) i
+  | a == F = travel s (Inst (heading s) v)
+
+run :: Program -> State
+run = foldl tick start

2020/12/Part1.hs

@@ -0,0 +1,10 @@
+#!/usr/bin/env runghc
+module Day12.Part1 where
+
+import Day12
+
+main = interact (show . solve . parseProgram)
+
+toList (a, b) = [a, b]
+
+solve = run

2020/12/input.txt

@@ -0,0 +1,788 @@
+W2
+F23
+S1
+W3
+L180
+W3
+R90
+N4
+F17
+S4
+W4
+R90
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+E1
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+W2
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+F34
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+F10
+S3
+W5
+S3
+F87
+

2020/12/small.txt

@@ -0,0 +1,5 @@
+F10
+N3
+F7
+R90
+F11

2020/13/Part1.hs

@@ -0,0 +1,17 @@
+#!/usr/bin/env runghc
+
+module Day13.Part1 where
+
+ts = 1000434
+bids = [17,41,983,29,19,23,397,37,13]
+
+waitTime ts bid = (ts `div` bid) * bid + bid - ts
+
+minimumBy fn (inp:inps) = minimumBy' fn inps inp
+  where
+    minimumBy' _ [] curr = curr
+    minimumBy' fn (x:xs) curr
+      | fn curr < fn x = minimumBy' fn xs curr
+      | otherwise = minimumBy' fn xs x
+
+main = putStrLn (show $ fst $ minimumBy snd $ zip bids $ map (waitTime ts) bids)

2020/README.md

@@ -12,12 +12,12 @@ asdf install
 
 ## Table of Contents
 
-|  S  |  M  |  T  |  W  |  T   |  F   |  S  |
-| :-: | :-: | :-: | :-: | :--: | :--: | :-: |
-|     |     | [1] | [2] | [3]  | [4]  | [5] |
-| [6] | [7] | [8] | [9] | [10] | [11] | 12  |
-| 13  | 14  | 15  | 16  |  17  |  18  | 19  |
-| 21  | 22  | 23  | 24  |  25  |      |     |
+|  S   |  M  |  T  |  W  |  T   |  F   |  S   |
+| :--: | :-: | :-: | :-: | :--: | :--: | :--: |
+|      |     | [1] | [2] | [3]  | [4]  | [5]  |
+| [6]  | [7] | [8] | [9] | [10] | [11] | [12] |
+| [13] | 14  | 15  | 16  |  17  |  18  |  19  |
+|  21  | 22  | 23  | 24  |  25  |      |      |
 
 [asdf]: https://asdf-vm.com/#/
 [haskell]: https://www.haskell.org
@@ -32,3 +32,5 @@ asdf install
 [9]: ./09
 [10]: ./10
 [11]: ./11
+[12]: ./12
+[13]: ./13