Grokking #219 - 1

    int traverse(TreeNode root) {
        int val = 0;

        if(root == null)
            return 0;

        if (root.left != null) {
            val += traverse(root.left.left) + traverse(root.left.right);
        }
        if (root.right != null) {
            val += traverse(root.right.left) + traverse(root.right.right);
        }

        return Math.max(val + root.val, traverse(root.left) + traverse(root.right));
    }

    public int rob(TreeNode root) {
        return traverse(root);
    }