pub fn day3_part1(input: &str) -> String {
    let batteries = parse(input);
    let sum: u64 = batteries.iter().map(|bank| max_joltage(bank, 2)).sum();
    sum.to_string()
}
pub fn day3_part2(input: &str) -> String {
    let batteries = parse(input);
    let sum: u64 = batteries.iter().map(|bank| max_joltage(bank, 12)).sum();
    sum.to_string()
}

fn max_joltage(bank: &[u8], battery_count: usize) -> u64 {
    let bank_length = bank.len();
    let mut digits = Vec::with_capacity(battery_count);
    let mut cursor = 0;
    for place in 0..battery_count {
        let range = cursor..bank_length - (battery_count - (place + 1));
        let (index_of_max_digit, max_digit) = bank[range]
            .iter()
            .enumerate()
            .max_by_key(|(index, digit)| (*digit, bank_length - index))
            .unwrap();
        cursor = index_of_max_digit + cursor + 1;
        digits.push(max_digit)
    }

    digits
        .iter()
        .fold(0, |acc, &&digit| acc * 10 + digit as u64)
}

fn parse(input: &str) -> Vec<Vec<u8>> {
    input
        .lines()
        .map(|bank| {
            bank.chars()
                .map(|c| c.to_digit(10).unwrap() as u8)
                .collect()
        })
        .collect()
}