29 lines
607 B
Haskell
29 lines
607 B
Haskell
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#!/usr/bin/env runghc
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import Day10
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import Data.Array
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import Data.IntSet (IntSet)
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import qualified Data.IntSet as IntSet
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main = interact (show . solve . parse)
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countPaths inp = pathsFrom start
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where
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start = IntSet.findMax inpSet + 3
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pathsFrom 0 = 1
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pathsFrom x
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| x < 0 = 0
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| IntSet.member x allowed =
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sum $ map ((!) memo) $ filter (>= 0) $ map ((-) x) [1, 2, 3]
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| otherwise = 0
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inpSet = IntSet.fromList inp
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allowed = IntSet.insert start inpSet
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memo = listArray bnds
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[ pathsFrom i | i <- range bnds ]
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bnds = (0, start)
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solve = countPaths
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