542f4ab0a0
* Adding binary search example for Haskell * Adding selection sort example in Haskell * Adding Haskell examples for chapter 3 * Adding examples for chapter 4 * Adding examples for chapter 5 * Adding git ignore * Add Haskell example for BFS * resetting * Adding haskell example for dijkstras algorithm * Adding Haskell example for chapter 8 * Adding power set based solution for set covering problem * Adding Haskell examples for chap 9
33 lines
1.0 KiB
Haskell
33 lines
1.0 KiB
Haskell
import Control.Applicative
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import Data.List
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import qualified Data.Set as Set
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import qualified Data.HashMap.Strict as Map
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stationsMap = Map.fromList [
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("kone", Set.fromList(["id", "nv", "ut"])),
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("ktwo", Set.fromList(["wa", "id", "mt"])),
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("kthree", Set.fromList(["or", "nv", "ca"])),
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("kfour", Set.fromList(["nv", "ut"])),
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("kfive", Set.fromList(["ca", "az"]))
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]
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statesNeeded = Set.fromList ["mt", "wa", "or", "id", "nv", "ut", "ca", "az"]
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powerSet xs = foldl (\acc x -> acc ++ (map (\e -> x:e) acc)) [[]] xs
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allStationCombinations = powerSet $ Map.keys stationsMap
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coverage stationsMap stations = map (`Map.lookup` stationsMap) stations
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stationsCoverage stations =
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fmap (Set.size . (Set.intersection statesNeeded)) $
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Just (foldl Set.union Set.empty ) <*>
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(sequence (coverage stationsMap stations))
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solution = foldl
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(\x y -> if stationsCoverage x >= stationsCoverage y then x else y)
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first
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rest
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where (first: rest) =
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sortBy (\a b -> compare (length a) (length b)) $
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(filter (not . null) allStationCombinations) |