226. Invert Binary Tree

Invert a binary tree.

     4
   /   
  2     7
 /    / 
1   3 6   9

     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.

 1 class Solution {
 2     public TreeNode invertTree(TreeNode root) {
 3         if(root==null) return null;
 4         TreeNode temp = new TreeNode(root.val);
 5         temp = root.left;
 6         root.left = root.right;
 7         root.right = temp;
 8         root.left = invertTree(root.left);
 9         root.right= invertTree(root.right);
10         return root;
11         
12     }
13 }