August 19, 2024
P62B - Collect the nodes at a given level in a list
A node of a binary tree is at level N if the path from the root to the node has length N-1. The root node is at level 1. Write a function atlevel to collect all nodes at a given level in a list.
(atlevel tree L) returns the list of nodes of the binary tree tree at level L
Using atlevel it is easy to construct a function levelorder which creates the level-order sequence of the nodes. However, there are more efficient ways to do that.
lisp
(defun atlevel (tree level)
(cond
((null tree) ())
((= level 1) (list tree))
(t (append (atlevel (second tree) (1- level))
(atlevel (third tree) (1- level))))
)
)
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