我希望以Newick 格式打印一棵二叉树,显示每个节点到其父节点的距离。目前我没有遇到以下代码的问题,它使用常规递归,但是树太深可能会产生堆栈溢出。
(defn tree->newick
[tree]
(let [{:keys [id children to-parent]} tree
dist (double to-parent)] ; to-parent may be a rational
(if children
(str "(" (tree->newick (first children))
"," (tree->newick (second children))
"):" dist)
(str (name id) ":" dist))))
(def example {:id nil :to-parent 0.0
:children [{:id nil :to-parent 0.5
:children [{:id "A" :to-parent 0.3 :children nil}
{:id "B" :to-parent 0.2 :children nil}]}
{:id "C" :to-parent 0.8 :children nil}]})
(tree->newick example)
;=> "((A:0.3,B:0.2):0.5,C:0.8):0.0"
(def linear-tree (->> {:id "bottom" :to-parent 0.1 :children nil}
(iterate #(hash-map :id nil :to-parent 0.1
:children [% {:id "side" :to-parent 0.1 :children nil}]))
(take 10000)
last))
(tree->newick linear-tree)
;=> StackOverflowError
我在当前实用程序(例如tree-seq
and clojure.walk
)中发现的问题是我必须多次访问内部节点,以插入逗号并关闭括号。我使用过clojure.zip
,但没有设法编写惰性/尾递归实现,因为我需要为每个内部节点存储它们已经被访问过的次数。