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  1. import Data.List
  2. main :: IO ()
  3. main = mapM_ (print . find4A) ["1 5 3 6 : 10", "1 5 3 6 7 : 10"]
  4. find4A :: String -> [String]
  5. find4A s = (flip (map . (!!)) =<< elemIndices y . map expr) $ combo [x1] opPlusDigitList
  6.   where
  7.     combo as []     = as
  8.     combo as (h:t)  = combo [a ++ b | a <- as, b <- h] t
  9.     opPlusDigitList = map (\x -> [op ++ x | op <- ops]) $ xs
  10.     (xs0, y0)       = break (==':') s
  11.     x1:xs           = words xs0
  12.     y               = read $ tail y0         :: Double
  13.     ops             = [" + ", " - ", " * ", " / "]
  14. expr :: String -> Double
  15. expr s = go (map read xxs) yys
  16.   where
  17.     (xxs, yys) = partition (`notElem` ["+", "-", "*", "/"]) $ words s
  18.     go [x1]       _        = x1
  19.     go (x1:x2:xs) ("*":ys) = go ((x1 * x2) : xs) ys
  20.     go (x1:x2:xs) ("/":ys) = go ((x1 / x2) : xs) ys
  21.     go (x1:xs)    ("+":ys) = x1 + go xs ys
  22.     go (x1:x2:xs) ("-":ys) = x1 + go ((-x2) : xs) ys
  23.     go _          _        = -1
  24.  
Success #stdin #stdout 0.01s 6352KB
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stdin
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Standard input is empty
stdout
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["1 + 5 * 3 - 6","1 * 5 / 3 * 6"]
["1 + 5 + 3 - 6 + 7"]
https://ideone.com/Ht2Hgp
language:
Haskell (ghc 8.4.4)
created:
11 years ago
visibility:
public

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