99 Clojure Problems – 62B: 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 method at-level to collect all nodes at a given level in a list."

(deftest p62b-at-level
  (is (= '(b c) (at-level '[a [b nil nil] [c [d nil nil] [e nil nil]]] 2))))

The basic idea for the solution was to see the tree as a list of nodes and to realise that the nodes at a given level start at node 2^(level - 1) and that this is also the size of each level. Solution on Github.

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99 Clojure Problems – 61A: Collect the Leaves of a Binary Tree in a List

"61A (*) Collect the leaves of a binary tree in a list. A leaf is a node with no successors. Write a method leaves to collect them in a list."

(deftest p61a-leaves
  (is (= '(b d e) (leaves '[a [b nil nil] [c [d nil nil] [e nil nil]]]))))

A variation on the previous exercise. Solution.

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99 Clojure Problems – 62: Collect the Internal Nodes of Binary Tree in a List

"An internal node of a binary tree has either one or two non-empty successors. Write a method internals to collect them in a list."

(deftest p62-internals
  (is (= '(a c) (internals '[a [b nil nil] [c [d nil nil] [e nil nil]]]))))

I used the same idea as in the two previous exercises: walk the tree and filter, just filtering for branch nodes this time. Again using a predicate I wrote earlier. Solution on Github.

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