2019.4.1

2019.4.1

//exercise 25.4
    public void preorderUsingStack(){
        preorderUsingStack(root);
    }

    private void preorderUsingStack(TreeNode<T> root){
        if(root == null)
            return;
        Stack<TreeNode<T>> stack = new Stack<>();
        stack.push(root);

        while (!stack.isEmpty()){
            TreeNode<T> current = stack.pop();
            System.out.print(current.element+" ");

            if(current.right != null){
                stack.push(current.right);
            }
            if(current.left != null){
                stack.push(current.left);
            }
        }
    }