fn main() {
    let input = include_str!("../input.txt").trim();

    let time = std::time::Instant::now();

    let mut memory = input.chars().enumerate()
        .map(|(i, c)| {
            if i % 2 == 0 {
                vec![Some(i as i32 / 2); c.to_string().parse::<usize>().unwrap()]
            } else {
                vec![None; c.to_string().parse::<usize>().unwrap()]
            }
        })
        .into_iter()
        .flatten()
        .collect::<Vec<Option<i32>>>();

    let mut j = memory.len() - 1;
    for i in 0..memory.len() {
        if j <= i {
            break;
        }
        if memory[i].is_some() {
            continue;
        }

        while memory[j].is_none() {
            j -= 1;
        }
        memory.swap(i, j);
        j -= 1;
    }

    let sum: i64 = memory.iter().enumerate().map(|(i, m)| {
        if let Some(s) = m {
            *s as i64 * i as i64
        } else {
            0_i64
        }
    }).sum();

    println!("Time elapsed: {:?}", time.elapsed());
    println!("Sum: {}", sum);
}