100-days-of-rust/Week-02/Day-10_Unique-Binary-Search-Trees/day10/src/lib.rs

pub fn catalan_number(n: u8) -> usize {
    let mut result = 1f64;

    for k in 2..=n {
        result *= (n as f64 + k as f64) / k as f64;
    }

    result.round() as usize
}