fun-with-digits.rs

    let x = 1930;
    let len = (x as f64).log10().floor() as u32 + 1;
    let mut digits = (0..len)
        .map(|i| (x / 10u64.pow(i)) % 10)
        .collect::<Vec<u64>>();
    digits.sort_unstable();
    let mut answer: u64 = 0;
    for (i, v) in digits.iter().enumerate() {
        answer += v * 10u64.pow(i as u32);
    }