我添加了两个帮助功能来拆分列表和添加tupples。 输出有两个不同的列表作为输入显示我的问题。
*主>快速排序[367,324,675,238,1237,345,12,45,1,434,2,1,33,43] [1,1,2,12,33,43,45,238,324,345,367,434,675,1237] - 有效
*主>快速排序[3687,324,675,238,1237,345,12,45,1,434,2,1,33,43] [3687,324,675,238,1237,345,12,45,1,434,2,1,33,43] - 不起作用
下面是代码:
splitBy :: Int -> [Int] -> ([Int],[Int])
splitBy n y = ([x|x <- y,x > n],[x|x <- y, x<=n])
addi :: ([a],[a]) -> ([a],[a]) -> ([a],[a])
addi ([],[]) ([],[]) = ([],[])
addi (x,y) (w,z) = (x++w,y++z)
splitBy' :: Int -> [Int] -> ([Int],[Int])
splitBy' _ [] = ([],[])
splitBy' n (y:ys) = addi (q,d) (splitBy' n ys)
where q = if y > n then [] else [y]
d = if y <= n then [] else [y]
addi' :: ([a],[a]) -> [a]
addi' ([],[]) = []
addi' (x,z) = x++z
quicksort :: [Int] -> [Int]
quicksort [] = []
quicksort (x:xs)
| (l1 /= [] ) && (l2 /= []) = addi'(quicksort l1', quicksort l2')
| l1 == [] = addi' (l1, quicksort l2)
| l2 == [] = addi' (l1,l2)
where
(l1,l2) = splitBy' x (x:xs)
(l1',l2') = (addi'(splitBy' (x-1) l1),addi' (splitBy' (x+1) l2))
答案 0 :(得分:9)
调试此类代码时,QuickCheck
是一个非常有用的工具。
我将您的代码放入Test.hs
,将其加载到ghci
然后运行:
*Test> import Test.QuickCheck
*Test Test.QuickCheck> quickCheck $ \xs -> quicksort xs == Data.List.sort xs
*** Failed! Falsifiable (after 8 tests and 5 shrinks):
[1,0]
*Test Test.QuickCheck> quicksort [1,0]
[1,0]
现在您有一个非常小的输入([1,0]
)来查看和跟踪您的代码:
quicksort (1::0::[]) -- has (l1,l2) = splitBy' 1 [1,0] = ([1,0],[])
= addi' ([1,0], []) -- because `l2 == []`
= [1,0] ++ []
= [1,0]
据推测,您对splitBy'
或quicksort
中的检查有不同的行为。检查此执行与您的意图的不同之处,您将找到如何修复代码。