非递归方式实现树的前序遍历（中序or后序）

用一个栈去存储要递归的内容

    public void preViewStack(){
        System.out.println("==test no digui==");
        Stack<Node> stack = new Stack<Node>();
        stack.push(root);
        Node tmp = null;
        while(!stack.isEmpty()) {
            tmp = stack.pop();
            System.out.println(tmp.value);
                
            if(tmp.rightNode != null) {
                stack.push(tmp.rightNode);
            }
            if(tmp.leftNode != null) {
                stack.push(tmp.leftNode);
            }
        }        
    }