[数据结构与算法]二叉树后序遍历-递归与非递归（左右根）

递归版本：

public static void reverseIn(Node head){
        if (head == null)
            return;
        reverseIn(head.left);
        reverseIn(head.right);
        System.out.print(head.value+",");
    }

非递归版本：

public static void unReverseIn(Node head){
        if (head != null){
            Stack<Node> stack1 = new Stack<>();
            Stack<Node> stack2 = new Stack<>();
            stack1.push(head);
            while (!stack1.isEmpty()){
                head = stack1.pop();
                stack2.push(head);
                if (head.left != null)
                    stack1.push(head.left);
                if (head.right != null)
                    stack1.push(head.right);
            }
            Node pop = null;
            while (!stack2.isEmpty()){
                pop = stack2.pop();
                System.out.print(pop.value+",");
            }

        }

    }