二叉树中序非递归遍历<超出内存限制>

代码如下

/**
* Definition for a binary tree node.
* public class TreeNode {
* int val;
* TreeNode left;
* TreeNode right;
* TreeNode() {}
* TreeNode(int val) { this.val = val; }
* TreeNode(int val, TreeNode left, TreeNode right) {
* this.val = val;
* this.left = left;
* this.right = right;
* }
* }
*/
class Solution {
    public List<Integer> inorderTraversal(TreeNode root) {
        LinkedList<Integer> res = new LinkedList<>();
        Stack<TreeNode> stack = new Stack<>();
        while(!stack.empty()||root!=null){
//首先不断吧左子节点放入，然后拿出来的时候判断有无右子节点，若有则取出再放入右子节点
            if(root!=null){
                stack.push(root);
            }
            while(root.left!= null){
                stack.push(root);
                root = root.left;
            }
            if(!stack.empty()){
                root = stack.pop();
                res.add(root.val);
            }
            if(root.right!=null){
//两个node
                root = root.right;
            }
        }
        return res;
    }
}

然后报 超出内存限制，没发现哪里循环了啊