haskell - Data.ByteString中的findSubstrings和breakSubstring

在Data/ByteString.hs的源代码中说，不赞成使用findSubstrings函数，而推荐使用breakSubstring。但是，我认为使用KMP算法实现的findSubstrings比幼稚的breakSubstring中使用的算法高效得多。有人知道为什么要这样做吗？

这是旧的实现:

{-# DEPRECATED findSubstrings "findSubstrings is deprecated in favour of breakSubstring." #-}

{-
{- This function uses the Knuth-Morris-Pratt string matching algorithm.  -}

findSubstrings pat@(PS _ _ m) str@(PS _ _ n) = search 0 0
where
  patc x = pat `unsafeIndex` x
  strc x = str `unsafeIndex` x

  -- maybe we should make kmpNext a UArray before using it in search?
  kmpNext = listArray (0,m) (-1:kmpNextL pat (-1))
  kmpNextL p _ | null p = []
  kmpNextL p j = let j' = next (unsafeHead p) j + 1
                     ps = unsafeTail p
                     x = if not (null ps) && unsafeHead ps == patc j'
                            then kmpNext Array.! j' else j'
                    in x:kmpNextL ps j'
  search i j = match ++ rest -- i: position in string, j: position in pattern
    where match = if j == m then [(i - j)] else []
          rest = if i == n then [] else search (i+1) (next (strc i) j + 1)
  next c j | j >= 0 && (j == m || c /= patc j) = next c (kmpNext Array.! j)
           | otherwise = j
-}

这是新的天真:

findSubstrings :: ByteString -- ^ String to search for.
           -> ByteString -- ^ String to seach in.
           -> [Int]
findSubstrings pat str
    | null pat         = [0 .. length str]
    | otherwise        = search 0 str
where
    STRICT2(search)
    search n s
        | null s             = []
        | pat `isPrefixOf` s = n : search (n+1) (unsafeTail s)
        | otherwise          =     search (n+1) (unsafeTail s)

最佳答案

进行更改的原因是，KMP的实现实际上比幼稚的版本效率低，而幼稚的版本只是着眼于性能。

关于haskell - Data.ByteString中的findSubstrings和breakSubstring，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/6331269/