相关疑难解决方法(0)

基本上我想将BST树变成一个映射,其中节点是键,节点的出现次数是值.所以,如果我输入这个:

toMap(叶子13)

我会的

> [(13,1)]

这是我到目前为止:

data Tree a = Empty | Node a (Tree a) (Tree a) deriving (Show)
leaf x = Node x Empty Empty

toMap' :: Int -> Tree a -> ([(a, Int)], Int)
toMap' a Empty = ([], a)
toMap' a (Node x xl xr) = ((x, a): xl' ++ xr', k)
                      where (xl', i) = toMap' (a+1) xl
                            (xr', k) = toMap' (i) xr

toMap :: Tree a -> [(a, Int)]
toMap = fst. toMap' …