题目链接
            
            
              java
              
              
            
          
          class Solution {
    List<Integer> res = new ArrayList<>();
    public void Inorder(TreeNode root) {
        if (root == null)
            return;
        Inorder(root.left);
        res.add(root.val);
        Inorder(root.right);
    }
    public List<Integer> inorderTraversal(TreeNode root) {
        Inorder(root);
        return res;
    }
}小结:秒了!!!