inorder_tree_traversal_2022.py

"""
Illustrate how to implement inorder traversal in binary search tree.
Author: Gurneet Singh
https://www.geeksforgeeks.org/tree-traversals-inorder-preorder-and-postorder/
"""


class BinaryTreeNode:
    """Defining the structure of BinaryTreeNode"""

    def __init__(self, data: int) -> None:
        self.data = data
        self.left_child = None
        self.right_child = None


def insert(node: None | BinaryTreeNode, new_value: int) -> BinaryTreeNode | None:
    """
    If the binary search tree is empty, make a new node and declare it as root.
    >>> node_a = BinaryTreeNode(12345)
    >>> node_b = insert(node_a, 67890)
    >>> node_a.left_child == node_b.left_child
    True
    >>> node_a.right_child == node_b.right_child
    True
    >>> node_a.data == node_b.data
    True
    """
    if node is None:
        node = BinaryTreeNode(new_value)
        return node

    # binary search tree is not empty,
    # so we will insert it into the tree
    # if new_value is less than value of data in node,
    #  add it to left subtree and proceed recursively
    if new_value < node.data:
        node.left_child = insert(node.left_child, new_value)
    else:
        # if new_value is greater than value of data in node,
        #  add it to right subtree and proceed recursively
        node.right_child = insert(node.right_child, new_value)
    return node


def inorder(node: None | BinaryTreeNode) -> None:  # if node is None,return
    """
    >>> inorder(make_tree())
    6
    10
    14
    15
    20
    25
    60
    """

    if node is None:
        return None
    # traverse left subtree
    inorder(node.left_child)
    # traverse current node
    print(node.data)
    # traverse right subtree
    inorder(node.right_child)


def make_tree() -> BinaryTreeNode | None:

    root = insert(None, 15)
    insert(root, 10)
    insert(root, 25)
    insert(root, 6)
    insert(root, 14)
    insert(root, 20)
    insert(root, 60)
    return root


def main() -> None:
    # main function
    root = make_tree()
    print("Printing values of binary search tree in Inorder Traversal.")
    inorder(root)


if __name__ == "__main__":
    import doctest

    doctest.testmod()
    main()