Binary Search Tree Inorder Traversal Algorithm (#6840)

* Binary Search Tree Inorder Traversal

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* Binary Search Tree Inorder Traversal v2

* Binary Search Tree Inorder Traversal

* Binary Search Tree Inorder Traversal

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* Update data_structures/binary_tree/inorder_tree_traversal_2022.py

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Co-authored-by: Christian Clauss <cclauss@me.com>

* Updated and removed print statement

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DIRECTORY.md

@@ -153,6 +153,7 @@
     * [Binary Tree Mirror](data_structures/binary_tree/binary_tree_mirror.py)
     * [Binary Tree Traversals](data_structures/binary_tree/binary_tree_traversals.py)
     * [Fenwick Tree](data_structures/binary_tree/fenwick_tree.py)
+    * [Inorder Tree Traversal 2022](data_structures/binary_tree/inorder_tree_traversal_2022.py)
     * [Lazy Segment Tree](data_structures/binary_tree/lazy_segment_tree.py)
     * [Lowest Common Ancestor](data_structures/binary_tree/lowest_common_ancestor.py)
     * [Maximum Fenwick Tree](data_structures/binary_tree/maximum_fenwick_tree.py)

data_structures/binary_tree/inorder_tree_traversal_2022.py

@@ -0,0 +1,83 @@
+"""
+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: BinaryTreeNode | None = None
+        self.right_child: BinaryTreeNode | None = None
+
+
+def insert(node: BinaryTreeNode | None, 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) -> list[int]:  # if node is None,return
+    """
+    >>> inorder(make_tree())
+    [6, 10, 14, 15, 20, 25, 60]
+    """
+    if node:
+        inorder_array = inorder(node.left_child)
+        inorder_array = inorder_array + [node.data]
+        inorder_array = inorder_array + inorder(node.right_child)
+    else:
+        inorder_array = []
+    return inorder_array
+
+
+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()