226. Invert Binary Tree

---

Invert a binary tree.

     4
   /   
  2     7
 /    / 
1   3 6   9

to

     4
   /   
  7     2
 /    / 
9   6 3   1

Trivia:
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 fuck off.

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