Anusha Murali

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Invert a Binary Tree

This is a simple problem from LeetCode (Problem #226).

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

Example 1:

binary_tree_1

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

Output: [4, 7, 2, 9, 6, 3, 1]

Example 2:

Input: root = []

Output: []

Solution

We can implement a simple solution using recursion as follows

# 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 root
        temp = self.invertTree(root.left)
        root.left = self.invertTree(root.right)
        root.right = temp
        return root

Runtime: Time complexity $O(n)$. Space complexity $O(n)$.

Back to Binary Tree Problems


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