;Task:
Implement a binary tree where each node carries an integer,   and implement:
:::*   pre-order,
:::*   in-order,
:::*   post-order,     and
:::*   level-order   [[wp:Tree traversal|traversal]].


Use those traversals to output the following tree:
          1
         / \
        /   \
       /     \
      2       3
     / \     /
    4   5   6
   /       / \
  7       8   9

The correct output should look like this:
 preorder:    1 2 4 7 5 3 6 8 9
 inorder:     7 4 2 5 1 8 6 9 3
 postorder:   7 4 5 2 8 9 6 3 1
 level-order: 1 2 3 4 5 6 7 8 9


;See also:
*   Wikipedia article:   [[wp:Tree traversal|Tree traversal]].
<br><br>