Count Numbers with Unique Digits

打表题，优化一下表就是O1 & O1

impl Solution {
    pub fn count_numbers_with_unique_digits(n: i32) -> i32 {
        use std::convert::TryInto;
        let n: usize = n.try_into().unwrap();
        let arr = [0, 1, 2, 6, 24, 120, 720, 5040, 40320, 362880, 3265920];
        let mut res = 0;
        for i in 0..=n {
            res += arr[10] / arr[10 - i];
        }
        res
    }
}