Generally speaking, each node in a basic tree can contain any number of children. However, in the case of binary trees, a node cannot contain more than two children. It means that it can contain zero, one, or two child nodes. Such a requirement has an important impact on the shape of a binary tree, as shown in the following two diagrams presenting binary trees:

As already mentioned, a node in a binary tree can contain at most two children. For this reason, they are referred to as the left child and right child. In the case of the binary tree shown on the left-hand side of the preceding diagram, node 21 has two children, 68 as the left child and 12 as the right child, while node 100 has only a left child.

Have you thought about how you can iterate through all the nodes in a tree? How can you specify an order of nodes during traversal of a tree? There are three common approaches: pre-order, in-order, and post-order, as shown in the following diagram:

As you can see in the diagram...