public void flatten(TreeNode root) {
		root = flattenRecursive(root)[0];
	}

	private TreeNode[] flattenRecursive(TreeNode node) {
		if (node.left == null && node.right == null ) return new TreeNode[] {node, node};
		TreeNode[] nodesLeft = flattenRecursive(node.left);
		TreeNode[] nodesRight = flattenRecursive(node.right);

		nodesLeft[1].right = nodesRight[0];

		node.right = nodesLeft[0];
		node.left = null;

		return new TreeNode[] { node, nodesRight[1]};
	}