226. Invert Binary Tree

Given the root of a binary tree, invert the tree, and return its root

Example 1:

• Input: root = [4,2,7,1,3,6,9]
• Output: [4,7,2,9,6,3,1]

Example 2:

• Input: root = [2,1,3]
• Output: [2,3,1]

Example 3:

• Input: root = []
• Output: []

Constraints:

• The number of nodes in the tree is in the range [0, 100].
• -100 <= Node.val <= 100

Approach

Solution

# 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

Explanation