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  1. -- Trie, yet another implementation
  2. -- (c) Vadim Vinnik, 2011
  3.  
  4. data Trie = Trie Bool [TrieEdge] deriving Show
  5. data TrieEdge = TrieEdge Char Trie deriving Show
  6.  
  7. trieEmpty = Trie False []
  8.  
  9. trieInsert :: Trie -> String -> Trie
  10. trieInsert (Trie _ l) [] = Trie True l
  11. trieInsert (Trie x l) s = Trie x (f l s) where
  12.     f [] (a:b) = [h a b]
  13.     f l1@(e@(TrieEdge c1 t):l2) s@(c2:s2)
  14.         | c1 == c2   = (TrieEdge c1 (trieInsert t s2)):l2
  15.         | c1  > c2   = (h c2 s2) : l1
  16.         | otherwise  = e : (f l2 s)
  17.     h a b = TrieEdge a (trieInsert trieEmpty b)
  18.  
  19. trieExists :: Trie -> String -> Bool
  20. trieExists (Trie x _) [] = x
  21. trieExists (Trie _ l) s = f l s where
  22.     f [] _ = False
  23.     f ((TrieEdge c1 t):l2) s@(c2:s2)
  24.         | c1 == c2   = trieExists t s2
  25.         | otherwise  = f l2 s
  26.  
  27. trieToString :: Trie -> String
  28. trieToString t = h t " " where
  29.     h (Trie x l) s = (if x then "#" else "") ++ '\n' : (foldl (++) "" (map f l)) where
  30.         f (TrieEdge c t) = (s ++ (c:[]) ++ (h t (" " ++ s)))
  31.  
  32. trieFromText :: String -> Trie
  33. trieFromText s = foldl trieInsert trieEmpty (words s)
  34.  
  35. trieAllWords :: Trie -> [String]
  36. trieAllWords (Trie x l) = (if x then "":r else r) where
  37.     r = foldl (++) [] (map f l) where
  38.         f (TrieEdge c t) = map (c:) (trieAllWords t)
  39.  
  40. trieEndings :: Trie -> String -> [String]
  41. trieEndings t [] = trieAllWords t
  42. trieEndings (Trie _ l) s = f l s where
  43.     f [] _ = []
  44.     f ((TrieEdge c1 t1):l1) s1@(c2:s2)
  45.         | c1 == c2  = trieEndings t1 s2
  46.         | c1  < c2  = f l1 s1
  47.         | otherwise = []
  48.  
  49. trieCompletions :: Trie -> String -> [String]
  50. trieCompletions t s = map (s++) (trieEndings t s)
  51.  
  52. main = do s <- getLine
  53.           let t = trieFromText s
  54.           putStr (trieToString t)
  55.           print (trieAllWords t)
  56.           print (trieEndings t "wh")
  57.           print (trieCompletions t "wi")
  58.  
stdin
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what which witch when where will wire wind window
compilation info 
[1 of 1] Compiling Main             ( prog.hs, prog.o )
Linking prog ...
stdout
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 w
  h
   a
    t#
   e
    n#
    r
     e#
   i
    c
     h#
  i
   l
    l#
   n
    d#
     o
      w#
   r
    e#
   t
    c
     h#
["what","when","where","which","will","wind","window","wire","witch"]
["at","en","ere","ich"]
["will","wind","window","wire","witch"]
https://ideone.com/lnbUn
language:
Haskell (ghc 8.4.4)
created:
12 years ago
visibility:
public

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