Source: 📖 Problem Solving with Algorithms and Data Structures using Python 7.7
Date: 2021-12-26
Preorder tree traversal is when a binary tree is traversed by first visiting the root node, then recursively doing a preorder traversal of the left node and then the right node.
The code, written as a function to which a binary tree is passed, is as follows:
def preorder_traversal(bin_tree):
if binary_tree:
print(binary_tree.key)
preorder_traversal(binary_tree.left_child)
preorder_traversal(binary_tree.right_child)
First, we check that the binary tree contains root data (a key value). If it does contain data, we print its data and then run the function again recursively on the left child and right child. This works because binary trees are fractal data types – when the left and right nodes are visited by the function, exactly the same structure will be found (or None, in which case the initial check is False and the function returns).