Invert Binary Tree (Leetcode 226)

It is also called as Mirror of a Binary Tree. Technique: FAITH technique of Recursion

Problem Link 1: https://leetcode.com/problems/invert-binary-tree/

Problem Link 2: https://practice.geeksforgeeks.org/problems/mirror-tree/1

Recursive Approach:

class Solution:

    def invertTree(self, root: Optional[TreeNode]) -> Optional[TreeNode]:
    
        if(root is None):
            return None
            
        l=self.invertTree(root.left)
        r=self.invertTree(root.right)
        root.left=r
        root.right=l
        
        return root

Iterative Approach (Using Stack):

class Solution:
    
    def invertTree(self, root: Optional[TreeNode]) -> Optional[TreeNode]:
        
        s=[root]
        
        while(len(s)>0):
            node=s.pop()
            if(node is not None):
                node.left,node.right=node.right,node.left
                s.append(node.left)
                s.append(node.right)
                
        return root