二叉树的中序遍历

public ArrayList<Integer> inorderTraversal(TreeNode root) {        Stack<TreeNode> stack = new Stack<TreeNode>();        ArrayList<Integer> result = new ArrayList<Integer>();        TreeNode curt = root;        while (curt != null || !stack.empty()) {            while (curt != null) {                stack.add(curt);                curt = curt.left;            }            curt = stack.peek();            stack.pop();            result.add(curt.val);            curt = curt.right;        }        return result;    }}