int run(TreeNode *root){

    if (root == nullptr) return ;

    if (root->left == nullptr)

    {

        return run(root->right) + ;

    }

    if (root->right == nullptr)

    {

        return run(root->left) + ;

    }

    int leftDepth = run(root->left);

    int rightDepth = run(root->right);

    return (leftDepth <= rightDepth) ? (leftDepth + ) : (rightDepth + );

}