49 lines
1.3 KiB
Haskell
49 lines
1.3 KiB
Haskell
{-# LANGUAGE OverloadedStrings #-}
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{-# LANGUAGE ViewPatterns #-}
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import Data.List (nub, scanl)
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import Data.Text (Text)
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import qualified Data.Text as T (lines, unpack, words)
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import qualified Data.Text.Read as T (decimal)
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import Lib (readFile')
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-- a rather slow program, takes 300 ms on my system (with `time`, but idc anymore 😭
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main :: IO ()
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main = do
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input <-
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concatMap
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((\[T.unpack -> [d], T.decimal -> Right (n, "")] -> replicate n d) . T.words)
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. T.lines
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<$> readFile' "day9.in"
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putStr "Q1: "
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print $ q 1 input
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putStr "Q2: "
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print $ q 9 input
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moveHead :: Char -> (Int, Int) -> (Int, Int)
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moveHead d (x, y) = case d of
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'L' -> (x - 1, y)
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'R' -> (x + 1, y)
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'U' -> (x, y + 1)
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'D' -> (x, y - 1)
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moveTail :: (Int, Int) -> (Int, Int) -> (Int, Int)
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moveTail (hx, hy) (tx, ty)
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| abs dx <= 1 && abs dy <= 1 = (tx, ty) -- dont move
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| abs dx > abs dy = (tx + signum dx, hy) -- move horizontally
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| abs dy > abs dx = (hx, ty + signum dy) -- move vertically
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| otherwise = (tx + signum dx, ty + signum dy ) -- move diagonally
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where
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dx = hx - tx
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dy = hy - ty
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q :: Int -> [Char] -> Int
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q n =
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length . nub . map last
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. scanl
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( \(h : t) d ->
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reverse $ foldl (\(h : xs) x -> moveTail h x : (h : xs)) [moveHead d h] t
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)
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(replicate (n + 1) (0, 0))
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