const ALLOWED_OPERATION_CHARS: &'static [char] = &[
'(', ')', '+', '-', '%', '/', '*'
];

fn main() {
    let text = String::from("2*(2*2)");
     let iter = text.chars().into_iter();
        iter.map(|x| {
            if ALLOWED_OPERATION_CHARS.iter().any(|y| y.to_owned() == iter.clone().next().unwrap_or(' ')) {
                format!("{} ", x)
            } else {
                x.to_string()
            }

        }).collect::<String>();
}