Invert Binary Tree

Invert a binary tree.

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

to

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

Java

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

        TreeNode temp = root.left;
        root.left = invertTree(root.right);
        root.right = invertTree(temp);

        return root;
    }
}