Find Leaves of Binary Tree

Given a binary tree, collect a tree’s nodes as if you were doing this: Collect and remove all leaves, repeat until the tree is empty.

Example:

Given binary tree

  1.           1
  2.          / \
  3.         2   3
  4.        / \     
  5.       4   5

Returns [4, 5, 3], [2], [1].

Explanation:

  1. Removing the leaves [4, 5, 3] would result in this tree:
    1.        1
    2.       / 
    3.      2
  2. Now removing the leaf [2] would result in this tree:
    1.        1
  3. Now removing the leaf [1] would result in the empty tree:
    1.        []

Returns [4, 5, 3], [2], [1].

Solution: