Leetcode - 226. Invert Binary Tree

Easy

Oct 06, 2025

#binary-tree

226. Invert Binary Tree

Problem

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

To solve this problem, we can use a recursive approach.

Our base case will be when the node has neither left or right children or the node itself is null, return here.

Otherwise, we set the left side to the right side and the right side to left side and then call the function on both left and right

Complexity

Time: O(n)

Iterate through the whole tree

Space: O(n)

For the recursive calls.

Solution

func invertTree(root *TreeNode) *TreeNode {
	if root == nil || (root.Left == nil && root.Right == nil) {
		return root
	}

	temp := root.Right
	root.Right = invertTree(root.Left)
	root.Left = invertTree(temp)
	return root
}