haskell - 遍历具有任意数量分支的树

Question

我想计算具有任意数量分支的树的最大度数。

data Tree a = Node a [Tree a]
  deriving (Eq, Show)

{-

       2
    /  |  \
   7   3   1
       |  / \
       0 3   2
 For this case: Answer will be 3. 
-}
tree1 :: Tree Int
tree1 = Node 2 [Node 7 [], Node 3 [Node 0 []], Node 1 [Node 3 [], Node 2 []]]

--I am doing something like this:

maxBranching :: Tree Int -> Int
maxBranching Node n [] = 1
maxBranching Node n xs = max (length xs) maxBranching xs

现在，我收到一个错误。我怎样才能编写正确的模式来解决这个问题？

Answer 1

首先，maxBranching 的参数类型是 Tree Int 而不是 [Tree Int] 并且您希望将所有子节点映射到它的最大度数，所以它应该是:

map maxBranching xs

不是

maxBranching xs

其次，参数需要放在括号中，否则，函数maxBranching就变成接受3个参数。

把它们全部写成:

maxBranching :: Tree Int -> Int
maxBranching (Node _ []) = 1
maxBranching (Node _ xs) =  maximum $ (length xs) : (map maxBranching xs)