Add Mirror a Binary Tree solution

data_structures/binary_tree/invert_binary_tree.py

@@ -0,0 +1,91 @@
+"""
+Given the root of a binary tree, invert the tree, and return its root.
+
+Leetcode problem reference: https://leetcode.com/problems/invert-binary-tree/
+"""
+
+from __future__ import annotations
+from typing import Optional
+
+
+class Node:
+    """
+    A Node has value variable and pointers to Nodes to its left and right.
+    """
+
+    def __init__(self, value: int) -> None:
+        self.value = value
+        self.left: Node | None = None
+        self.right: Node | None = None
+
+
+def get_tree_inorder(tree: Optional[Node], tree_list: list = None) -> list:  
+    """
+    Prints the inorder traversal of a tree
+    """
+    if tree_list is None:
+        tree_list = []
+
+    if tree:
+        get_tree_inorder(tree.left, tree_list)
+        tree_list.append(tree.value)
+        get_tree_inorder(tree.right, tree_list)
+
+    return tree_list
+
+def invert_binary_tree(root: Optional[Node]) -> None:
+
+    r"""
+    The tree looks like this
+          1
+         /  \
+        2    3
+       / \    \
+      4   5    6
+     / \   \
+    7   8   9
+
+
+    >>> tree = Node(1)
+    >>> tree.left = Node(2)
+    >>> tree.right = Node(3)
+    >>> tree.left.left = Node(4)
+    >>> tree.left.right = Node(5)
+    >>> tree.right.right = Node(6)
+    >>> tree.left.left.left = Node(7)
+    >>> tree.left.left.right = Node(8)
+    >>> tree.left.right.right = Node(9)
+
+    >>> get_tree_inorder(tree)
+    [7, 4, 8, 2, 5, 9, 1, 3, 6]
+    >>> inverted_tree = invert_binary_tree(tree)
+    >>> get_tree_inorder(inverted_tree)
+    [6, 3, 1, 9, 5, 2, 8, 4, 7]
+
+    The inverted tree looks like this
+          1
+         /  \
+        3    2
+       /    / \    
+      6    5   4    
+          /   / \      
+         9   8   7   
+    """
+
+
+    if root != None: #If root is not None
+            temp : Node = root.left  #Save left Node in a temp variable
+            # Swap the Nodes
+            root.left = root.right 
+            root.right = temp
+            # Now, invoke the function recursively for both the children
+            invert_binary_tree(root.left) 
+            invert_binary_tree(root.right)
+    # Return the Node
+    return root
+
+
+if __name__ == "__main__":
+
+    import doctest
+    doctest.testmod()