rustlings/exercises/iterators/iterators4.rs

// iterators4.rs
// Execute `rustlings hint iterators4` or use the `hint` watch subcommand for a hint.


pub fn factorial(num: u64) -> u64 {
    // let mut product: u64 = 1;
    // for i in 2..num+1 {
    //     product *= i;
    // }
    // product
        (2..num+1).into_iter().fold(1, |acc, x| x * acc)
    
    // Complete this function to return the factorial of num
    // Do not use:
    // - return
    // Try not to use:
    // - imperative style loops (for, while)
    // - additional variables
    // For an extra challenge, don't use:
    // - recursion
    // Execute `rustlings hint iterators4` for hints.
}

#[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));
    }
}