226. Invert Binary Tree

Invert a binary tree.

Example:

Input:

     4
   /   \
  2     7
 / \   / \
1   3 6   9

Output:

     4
   /   \
  7     2
 / \   / \
9   6 3   1

Important:
This problem was inspired by this original tweet by Max Howell:

    Google: 90% of our engineers use the software you wrote (Homebrew), but you can’t invert a binary tree on a whiteboard so f*** off.
  • Easy

public TreeNode invertTree(TreeNode root) {
    if(root == null) return null;
    TreeNode temp = root.left;
    root.left = root.right;
    root.right = temp;
    invertTree(root.right);
    invertTree(root.left);
    return root;
}