32 lines
1.6 KiB
Haskell
32 lines
1.6 KiB
Haskell
module Part1 where
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import Commons
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import Data.Array (Ix (inRange), bounds, (!))
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cleanNext :: Trails -> [(Int, Int)] -> [((Int, Int), Direction)] -> [((Int, Int), Direction)]
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cleanNext tr hist [] = []
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cleanNext tr hist ((ch, dh): t) =
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if inRange (bounds tr) ch && (tr ! ch == Slope dh || tr ! ch == Empty) && notElem ch hist
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then (ch, dh): cleanNext tr hist t else cleanNext tr hist t
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getNext :: Trails -> [(Int, Int)] -> Direction -> [((Int, Int), Direction)]
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getNext tr ((y, x): t) North = cleanNext tr t [((y - 1, x), North), ((y, x - 1), West), ((y, x + 1), East)]
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getNext tr ((y, x): t) East = cleanNext tr t [((y - 1, x), North), ((y, x + 1), East), ((y + 1, x), South)]
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getNext tr ((y, x): t) South = cleanNext tr t [((y + 1, x), South), ((y, x - 1), West), ((y, x + 1), East)]
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getNext tr ((y, x): t) West = cleanNext tr t [((y - 1, x), North), ((y, x - 1), West), ((y + 1, x), South)]
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getNextTrails' :: Trails -> (Int, Int) -> (Int, Int) -> [(Int, Int)] -> [((Int, Int), Direction)] -> [[(Int, Int)]]
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getNextTrails' _ _ _ _ [] = []
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getNextTrails' tr f s hist ((ch, dh): t)
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| ch == f = hist: getNextTrails' tr f ch hist t
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| otherwise = getNextTrails tr f ch (ch: hist) dh ++ getNextTrails' tr f ch hist t
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getNextTrails :: Trails -> (Int, Int) -> (Int, Int) -> [(Int, Int)] -> Direction -> [[(Int, Int)]]
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getNextTrails tr f s hist d = let next = getNext tr hist d
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in getNextTrails' tr f s hist next
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getAllTrails :: Trails -> [[(Int, Int)]]
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getAllTrails tr = let ((yMin, xMin), (yMax, xMax)) = bounds tr
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in getNextTrails tr (yMax, xMax - 1) (yMin, xMin + 1) [(yMin, xMin + 1)] South
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