rustlings/exercises/18_iterators/iterators4.rs

fn factorial(num: u64) -> u64 {
    // Complete this function to return the factorial of num
    // Do not use:
    // - early returns (using the `return` keyword explicitly)
    // Try not to use:
    // - imperative style loops (for, while)
    // - additional variables
    // For an extra challenge, don't use:
    // - recursion
}

fn main() {
    // You can optionally experiment here.
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn factorial_of_0() {
        assert_eq!(1, factorial(0));
    }

    #[test]
    fn factorial_of_1() {
        assert_eq!(1, factorial(1));
    }
    #[test]
    fn factorial_of_2() {
        assert_eq!(2, factorial(2));
    }

    #[test]
    fn factorial_of_4() {
        assert_eq!(24, factorial(4));
    }
}