我有问题,我不知道如何决定我的函数indexJ
必须在每个步骤中选择什么子树遍历我的平衡二叉树 - JoinList
。平衡二叉树的索引函数
这个想法是给缓存每个子树的大小(数据元素的数量)。然后可以在每个步骤中使用它来确定所需的索引是在左边还是右边。
我有这样的代码:
data JoinList m a = Empty
| Single m a
| Append m (JoinList m a) (JoinList m a)
deriving (Eq, Show)
newtype Size = Size Int
deriving (Eq, Ord, Show, Num)
getSize :: Size -> Int
getSize (Size i) = i
class Sized a where
size :: a -> Size
instance Sized Size where
size = id
instance Monoid Size where
mempty = Size 0
mappend = (+)
我写功能:
tag :: Monoid m => JoinList m a -> m
tag Empty = mempty
tag (Single x dt) = x
tag (Append x l_list r_list) = x
(+++) :: Monoid m => JoinList m a -> JoinList m a -> JoinList m a
(+++) jl1 jl2 = Append (mappend (tag jl1) (tag jl2)) jl1 jl2
indexJ :: (Sized b, Monoid b) => Int -> JoinList b a -> Maybe a
indexJ _ Empty = Nothing
indexJ i jl | i < 0 || (i+1) > (sizeJl jl) = Nothing
where sizeJl = getSize . size . tag
indexJ 0 (Single m d) = Just d
indexJ 0 (Append m (Single sz1 dt1) jl2) = Just dt1
indexJ i (Append m jl1 jl2) = if (sizeJl jl1) >= (sizeJl jl2)
then indexJ (i-1) jl1
else indexJ (i-1) jl2
where sizeJl = getSize . size . tag
功能tag
和(+++)
运作良好,但我需要完成indexJ
功能,它必须返回从第i个元素我的JoinList树,i = [0..n]
我的功能indexJ
working wrong =) 如果我有空树 - 它是(大小0) 如果我有单一(大小1)“数据” - 它的(大小1) 但如果我有附加(大小2)(单(大小1)'k ')(单(1)'''')我必须选择哪个分支? i-1 = 1,我有两个分支,每个分支有1个数据元素。
UPDATE:如果有人需要采取抗摔功能JoinList的树木 我让它:
dropJ :: (Sized b, Monoid b) => Int -> JoinList b a -> JoinList b a
dropJ _ Empty = Empty
dropJ n jl | n <= 0 = jl
dropJ n jl | n >= (getSize . size $ tag jl) = Empty
dropJ n (Append m jL1 jL2)
| n == s1 = jL2
| n < s1 = (dropJ n jL1) +++ jL2
| otherwise = dropJ (n - s1) jL2
where s1 = getSize . size $ tag jL1
takeJ :: (Sized b, Monoid b) => Int -> JoinList b a -> JoinList b a
takeJ _ Empty = Empty
takeJ n jl | n <= 0 = Empty
takeJ n jl | n >= (getSize . size $ tag jl) = jl
takeJ n (Append m jL1 jL2)
| n == s1 = jL1
| n < s1 = (takeJ n jL1)
| otherwise = jL1 +++ takeJ (n - s1) jL2
where s1 = getSize . size $ tag jL1
谢谢!您的版本正常工作。我使用1,2,3,4和8个数据元素在JoinLists上测试它=) – 2013-05-11 13:28:21