Question

Complete binary tree: A complete binary tree is a binary tree in which every level, except possibly the last, is completely filled, and all nodes are as far left as possible.

How to: traverse in order recursively a tree like this?

    1
  2   3
4  5 

Where 2 and 3 is a node of 1 and 4 and 5 is a node of 2.

Answer 1

For tree-traversal there are basically 3 algorithms

Preorder, Inorder and Postorder

void inorder(root_node)
{
    if(root_node != null)
    {
        inorder(root_node->left);
        println(root_node->value);
        inorder(root_node->right);
    }
}

Output: 4 2 5 1 3

You can refer this link for more details.

EDIT:

To answer your question (in comments section), If you want to traverse all the nodes acc. to their level in tree, you should use graph traversal algorithms. in your case it’ll be BFS – Breadth First Search.

(Note: tree is also a kind of graph)

See here for details.