226. Invert Binary Tree

At a Glance

• Topic: Binary Tree
• Pattern: DFS
• Difficulty: Easy
• LeetCode: 226

Problem Statement

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 Steps

Use a recursive DFS approach. For each node, swap its left and right children, then recursively call the function on the left and right subtrees.

Optimal JS Solution

function invertTree(root) {
  if (!root) return null;
  const temp = root.left;
  root.left = invertTree(root.right);
  root.right = invertTree(temp);
  return root;
}

Edge Cases & Pitfalls

• Always consider empty or null inputs.
• Watch out for off-by-one index errors.