*86*

# Pre-order traversal

## Steps

- Visit the root node
- traverse the left sub-tree in pre-order
- traverse the right sub-tree in pre-order

## Algorithm

**Step 1:**Repeat Steps 2 to 4 while TREE != NULL**Step 2:**Write TREE -> DATA**Step 3:**PREORDER(TREE -> LEFT)**Step 4:**PREORDER(TREE -> RIGHT)

[END OF LOOP]**Step 5:**END

## C Function

### Example

Traverse the following binary tree by using 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.

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