Binary Tree Preorder Traversal

Step 1: Repeat Steps 2 to 4 while TREE != NULL
Step 2: Write TREE -&gt; DATA
Step 3: PREORDER(TREE -&gt; LEFT)
Step 4: PREORDER(TREE -&gt; RIGHT) [END OF LOOP]
Step 5: END

Pre-order traversal

  void pre-order(struct treenode *tree)  {  if(tree != NULL)  {  printf(“%d”,tree→ root);  pre-order(tree→ left);  pre-order(tree→ right);  }  }  

Traverse the following binary tree by using pre-order traversal

binary tree Pre-order traversal

Since, the traversal scheme, we are using is pre-order traversal, therefore, the first element to be printed is 18.
traverse the left sub-tree recursively. The root node of the left sub-tree is 211, print it and move to left.
Left is empty therefore print the right children and move to the right sub-tree of the root.
20 is the root of sub-tree therefore, print it and move to its left. Since left sub-tree is empty therefore move to the right and print the only element present there i.e. 190.
Therefore, the printing sequence will be 18, 211, 90, 20, 190.