# What Is Preorder Traversal in Data Structure?

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Heather Bennett

In data structure, preorder traversal is a method used to traverse and visit every node in a binary tree. It is a depth-first traversal technique where the root node is visited first, followed by the left subtree, and then the right subtree.

## Understanding Preorder Traversal

Preorder traversal follows a specific order to visit each node in a binary tree. The process can be summarized as follows:

• Visit the root node: In preorder traversal, we start by visiting the root node of the binary tree.
• Traverse the left subtree: After visiting the root node, we move to the left subtree and perform a preorder traversal on it.
• Traverse the right subtree: Once we finish traversing the entire left subtree, we move to the right subtree and perform a preorder traversal on it.

## An Example of Preorder Traversal

To better understand how preorder traversal works, let’s consider an example of a binary tree:

```        1
/ \
2   3
/ \   \
4   5   6
```

If we perform a preorder traversal on this binary tree, the order in which nodes are visited would be:

1. Visit node 1 (root)
2. Visit node 2 (left child of root)
3. Visit node 4 (left child of node 2)
4. Visit node 5 (right child of node 2)
5. Visit node 3 (right child of root)
6. Visit node 6 (right child of node 3)

## Implementing Preorder Traversal

To implement preorder traversal, we can use recursion or iteration. Here’s an example of how to implement it using recursion in Python:

```def preorderTraversal(node):
if node is None:
return

# Visit the root node
print(node.value)

# Traverse the left subtree
preorderTraversal(node.left)

# Traverse the right subtree
preorderTraversal(node.right)
```

This recursive implementation follows the same logic as described earlier. It first visits the root node, then recursively performs a preorder traversal on the left and right subtrees.

## Conclusion

Preorder traversal is a fundamental method for visiting nodes in a binary tree. By understanding its order and implementing it correctly, you can effectively traverse and process every node in a tree data structure.