Haskell树列出-预遍遍 [英] Haskell Tree to List - preorder traversal

问题描述

在Haskell中给出以下树结构:

Given the following tree structure in Haskell:

data Tree = Leaf Int | Node Int Tree Tree deriving Show

如何让Haskell以预定顺序返回数据列表?

How can I get Haskell to return a list of the data in pre-order?

例如给出一棵树:

Node 1 (Leaf 2) (Leaf 3)

返回类似的内容:

preorder = [1,2,3]

推荐答案

好的，很抱歉收到的答复很晚，但我的工作方式如下:

Ok, sorry about the late reply, but I got this working as follows:

preorder(Leaf n) = [n]
preorder(Node n treeL treeR) = [n] ++ preorder treeL ++ preorder treeR'code'

但这仍然不适用于我

preorder (Leaf n) = [n]   
preorder (Node n a b) = n:(preorder a) ++ (preorder b) 

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