Invert Binary Tree is one of the most popular programming problems. It’s an easy problem. I assume that you have a basic understanding of Binary Tree and Recursion.

The problem description is straightforward. Simply put, we have to invert a binary tree and then return the root.

More precisely, to solve this, we need to swap the left subtree with the right subtree of a node. And we have to do this swapping in every step. We will solve this problem recursively. The algorithm we will use is DFS.

Let’s see the solution in Python.

# Definition for a binary tree node. # class TreeNode: # def __init__(self, val=0, left=None, right=None): # self.val = val # self.left = left # self.right = right class Solution: def invertTree(self, root: Optional[TreeNode]) -> Optional[TreeNode]: if not root: return None left = self.invertTree(root.left) right = self.invertTree(root.right) root.left = right root.right = left return root

The time complexity of this problem is **O(n)**, where **n** is the number of nodes. And space complexity is also **O(n)**. This **n** is the number stack size in the memory for recursive function calls.