pub fn hint_weight(hint: &[u8], max_ones: usize, rows: usize) -> Option<usize> {
    let mut previous = 0usize;
    let mut total = 0usize;
    let mut bad = false;
    let mut i = 0usize;
    while i < rows {
        let current = hint[max_ones + i] as usize;
        if current < previous || current > max_ones {
            bad = true;
        } else {
            let mut j = previous;
            while j < current {
                total += hint[j] as usize;
                j += 1;
            }
            previous = current;
        }
        i += 1;
    }
    if bad { None } else { Some(total) }
}