// comment
fn main() {
    let one = 5;
    let two = 34; //не выдержал 130

    println!("Hello, factorial {}!", two);
    println!("prod:    {}\ntailrec: {}\nand rec: {}", prod(two), tailrec(two), rec(two));
    println!("–––––\n{}: {}", one, prod(one));

}

fn prod(n: u128) -> u128 {
    n < 2 && return 1;
    let mut acc = *&mut 1;
    //let mut ptr = *acc;
    for i in 2..n + 1 {
        acc *= i;
    }
    acc
}

fn tailrec(n: u128) -> u128 {
    return _helper(1, n);

    fn _helper(acc: u128, n: u128) -> u128 {
        if n > 1 {
            //println!("*** {},{}", acc * n, n - 1);
            _helper(acc * n, n - 1)
        } else {
            //println!("result is {}\n", acc);
            acc
        }
    }
}

fn rec(n: u128) -> u128 {
    if n > 1 {
        n * rec(n - 1)
    } else {
        1
    }
}