@@ -311,34 +311,58 @@ hanoi n start temp end =
311311 bottom-up solution p356
312312-}
313313genPerm :: String -> [String
314- genPerm = genPermHelper [[] ]
314+ genPerm chars = genPermHelper [[] ] listStr
315+ where listStr = map (: [] ) chars
315316
316- -- Loop through all possible character
317- genPermHelper :: [String -> String -> [String
317+ -- Loop through all possible characters/strings
318+ genPermHelper :: [String -> [ String ] -> [String
318319genPermHelper inp [] = inp
319320genPermHelper inp (x: xs) = genPermHelper newInp xs
320- where newInp = appendPerm inp x
321- 322- -- Accumulate new permutations (not finished)
323- appendPerm :: [String -> Char -> [String
324- appendPerm [] _ = []
325- appendPerm (x: xs) c = newPerm ++ appendPerm xs c
326- where -- newPerm = appendPermHelper x c 0 -- with duplicates
327- newPerm = appendPermHelper' x c 0 [] -- without duplicates
328- 329- -- Insert the character to every index of the input
330- appendPermHelper :: String -> Char -> Nat -> [String
321+ where newInp = appendPerm inp x []
322+ 323+ -- Accumulate new permutations base on the string (not finished)
324+ appendPerm :: [String -> String -> [String -> [String
325+ appendPerm [] _ acc = acc
326+ appendPerm (x: xs) c acc = appendPerm xs c (acc++ newPerm)
327+ where -- newPerm = complement acc (appendPermHelper x c 0) -- with duplicates
328+ newPerm = complement acc (appendPermHelper' x c 0 [] ) -- without duplicates
329+ 330+ -- another check for duplicates in appendPerm level,
331+ -- this need to work with appendPermHelper'
332+ complement :: [String -> [String -> [String
333+ complement _ [] = []
334+ complement a (x: xs)
335+ | x `elem` a = complement a xs
336+ | otherwise = x: complement a xs
337+ 338+ -- Insert the character/string to every index of the input
339+ appendPermHelper :: String -> String -> Nat -> [String
331340appendPermHelper str c ind
332341 | ind > length str = []
333- | otherwise = (fstHalf ++ [c] ++ sndHalf): appendPermHelper str c (ind+ 1 )
342+ | otherwise = (fstHalf ++ c ++ sndHalf): appendPermHelper str c (ind+ 1 )
334343 where (fstHalf,sndHalf) = splitAt ind str
335344
336- -- Insert the character to every index of the input with no duplicates
337- appendPermHelper' :: String -> Char -> Nat -> [String -> [String
345+ -- Insert the character/string to every index of the input with no duplicates
346+ appendPermHelper' :: String -> String -> Nat -> [String -> [String
338347appendPermHelper' str c ind acc
339348 | ind > length str = acc
340349 | newPerm `elem` acc = appendPermHelper' str c (ind+ 1 ) acc
341350 | otherwise = appendPermHelper' str c (ind+ 1 ) (newPerm: acc)
342351 where (fstHalf,sndHalf) = splitAt ind str
343- newPerm = fstHalf ++ [c] ++ sndHalf
352+ newPerm = fstHalf ++ c ++ sndHalf
353+ 354+ {-
355+ 8.9
356+ Implement an algorithm to print all valid (eg: properly opened and closed)
357+ combinations of n pairs of parentheses.
358+
359+ test case: genPerm' ["()","()","()"]
360+
361+ modify the genPerm from 8.7 and 8.8 to make it works for string, and remove
362+ duplicates in two different levels.
363+ -}
364+ paren :: String
365+ paren = " ()"
344366
367+ genPerm' :: [String -> [String
368+ genPerm' = genPermHelper [[] ]
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