Preorder Binary Tree Traversal

Question

I need help in Preorder Binary Tree Traversal I understand how it travels (root, left, right) but look at that example (a)

Why did they write it this way? According to the rule, we should go to *, but it went to 2 Is it because 2 have no children?

Answer 1

Preorder binary tree traversal algorithm:

1. Visit the root.
2. Traverse the left subtree, i.e., call Preorder(left-subtree)
3. Traverse the right subtree, i.e., call Preorder(right-subtree);

Thus, first you traverse the root + then go to step 2 and visit the left subtree -, and then the traversal algorithm is called again from - root and the algorithm takes the first its step, but now its root is -. After the first step algorithm go to step 2, and its left subtree is 2, and e.t.c.

So, for you better understanding you might look this video Tree Traversals