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milkywayw Sep 17th, 2019 130 Never
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  1. data State = LeftSide | LeftPeriod | AtSymbol | RightSide | RightPeriod | End
  2.    
  3. correctEmails pattern
  4.     | isValid pattern = rawr LeftPeriod pattern
  5.     | otherwise = 0
  6.     where isValid str = all (\x -> elem x "abcde?@.") str
  7.  
  8. -- |
  9.  
  10. rawr :: State -> String -> Int
  11.  
  12. rawr End [] = 1
  13. rawr _ [] = 0
  14.  
  15. rawr state ('?':xs) = sum [rawr state (y:xs) | y <- (allowedChars state)] + 5 * rawr state ('a':xs)
  16.  
  17. rawr LeftSide ('@':xs) = rawr AtSymbol xs
  18. rawr LeftSide ('.':xs) = rawr LeftPeriod xs
  19. rawr LeftSide ( _ :xs) = rawr LeftSide xs
  20.  
  21. rawr LeftPeriod ('@': xs) = 0
  22. rawr LeftPeriod ('.': xs) = 0
  23. rawr LeftPeriod ( _ : xs) = rawr LeftSide xs
  24.  
  25. rawr AtSymbol ('@':xs) = 0
  26. rawr AtSymbol ('.':xs) = 0
  27. rawr AtSymbol ( _ :xs) = rawr RightSide xs
  28.  
  29. rawr RightSide ('@':xs) = 0
  30. rawr RightSide ('.':xs) = rawr RightPeriod xs
  31. rawr RightSide ( _ :xs) = rawr RightSide xs
  32.  
  33. rawr RightPeriod ('@':xs) = 0
  34. rawr RightPeriod ('.':xs) = 0
  35. rawr RightPeriod ( _ :xs) = rawr End xs
  36.  
  37. rawr End ('@':xs) = 0
  38. rawr End ('.':xs) = rawr RightPeriod xs
  39. rawr End ( _ :xs) = rawr End xs
  40.  
  41. -- |
  42.  
  43. allowedChars :: State -> [Char]
  44. allowedChars LeftSide = "@."
  45. allowedChars RightSide = "."
  46. allowedChars End = "."
  47. allowedChars _ = []
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