Symmetric tree

data_structures/binary_tree/symmetric_tree.py

@@ -0,0 +1,85 @@
+"""
+Given the root of a binary tree, check whether it is a mirror of itself
+(i.e., symmetric around its center).
+
+Leetcode reference: https://leetcode.com/problems/symmetric-tree/
+"""
+
+
+class Node:
+    """
+    A Node has data variable and pointers to Nodes to its left and right.
+    """
+
+    def __init__(self, data: int) -> None:
+        self.data = data
+        self.left: Node | None = None
+        self.right: Node | None = None
+
+
+class SymmetricTree:
+    def is_symmetric_tree(self, tree: Node) -> bool:
+        r"""
+        Test cases for is_symmetric_tree function.
+
+        The below tree looks like this
+               1
+             /   \
+            2      2
+           / \    / \
+          3   4   4  3
+
+        >>> tree = Node(1)
+        >>> tree.left = Node(2)
+        >>> tree.right = Node(2)
+        >>> tree.left.left = Node(3)
+        >>> tree.left.right = Node(4)
+        >>> tree.right.left = Node(4)
+        >>> tree.right.right = Node(3)
+
+        >>> SymmetricTree().is_symmetric_tree(tree)
+        True
+
+        The below tree looks like this
+              1
+            /   \
+          2      2
+         / \    / \
+        3   4   3  4
+
+        >>> tree2 = Node(1)
+        >>> tree2.left = Node(2)
+        >>> tree2.right = Node(2)
+        >>> tree2.left.left = Node(3)
+        >>> tree2.left.right = Node(4)
+        >>> tree2.right.left = Node(3)
+        >>> tree2.right.right = Node(4)
+
+        >>> SymmetricTree().is_symmetric_tree(tree2)
+        False
+        """
+        if tree is None:
+            # An empty tree is considered symmetric.
+            return True
+        return self.is_mirror(tree.left, tree.right)
+
+    @staticmethod
+    def is_mirror(self, left, right) -> bool:
+        if left is None and right is None:
+            # Both sides are empty, which is symmetric.
+            return True
+        if left is None or right is None:
+            # One side is empty while the other is not, which is not symmetric.
+            return False
+        if left.data == right.data:
+            # The values match, so check the subtree
+            return self.is_mirror(left.left, right.right) and self.is_mirror(
+                left.right, right.left
+            )
+        return False
+
+
+if __name__ == "__main__":
+    from doctest import testmod
+
+    testmod()