巴别诺瓦

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Haskell 趣题：树的遍历

Mon, 2008/10/06 - 22:28 — code17

很经典的老题了，说不定很多教材里都有，最近在好几个地方又见着了，所以在这里贴一下。

设一棵树的类型为：

data Tree t = Leaf t

            | Node t (Tree t) (Tree t)

              deriving (Show)

写一函数 avgTree :: (Fractional t) => Tree t -> Tree t，将树中所有节点中的值 (即类型为 t 的那些值) 全部替换为它们的均值。常见的方法是遍历这棵树取均值、再遍历一次 mirror 这棵树以构造新树，这里的要求是只遍历一次。

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Tue, 2008/10/07 - 10:00 — roy_hu

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Tue, 2008/10/07 - 16:52 — code17

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Fri, 2008/10/10 - 12:56 — fishmacs

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Tue, 2008/10/14 - 14:37 — chylli