Programming Challenge - Rust - Roman Numerals Checkpoint 2

main.rs

// associate a roman numeral with its value
struct RomanNumeral {
    txt: String,
    value: i32,
}

fn is_factor_of_ten(i: i32) -> bool {
    if i == 1 {
        return true;
    }

    let div_ten = i / 10;

    // values will floor to zero if they're not a factor of 10
    if div_ten == 0 {
        return false;
    }

    return is_factor_of_ten(div_ten);
}

fn subtractor_value(desc_numerals: &Vec<RomanNumeral>, current_pos: usize) -> Option<RomanNumeral> {
    let curr = desc_numerals.get(current_pos).unwrap();
    let mut next_numeral = String::new();

    match desc_numerals.get(current_pos + 1) {
        None => {
            return None;
        },
        Some(next_rn) => {
            if is_factor_of_ten(next_rn.value) {
                next_numeral.push_str(&next_rn.txt);
                next_numeral.push_str(&curr.txt);
                return Some(RomanNumeral{
                    txt: next_numeral,
                    value: curr.value - next_rn.value
                });
            }

            match desc_numerals.get(current_pos + 2) {
                None => None,
                Some(next2_rn) => {
                    if is_factor_of_ten(next2_rn.value) {
                        next_numeral.push_str(&next2_rn.txt);
                        next_numeral.push_str(&curr.txt);
                        return Some(RomanNumeral{
                            txt: next_numeral,
                            value: curr.value - next2_rn.value
                        });
                    }
                    return None;
                }
            }
        }
    }
}