pub fn day1() {
    let input = crate::input(1);

    let (mut left, mut right): (Vec<u64>, Vec<u64>) = input
        .lines()
        .filter(|line| !line.is_empty())
        .map(|line| {
            let nums: Vec<&str> = line.split_whitespace().collect();
            (
                nums[0].parse::<u64>().expect("Invalid left number"),
                nums[1].parse::<u64>().expect("Invalid right number")
            )
        })
        .unzip();
    println!("Found {} number pairs.", left.len());

    left.sort();
    right.sort();

    let differences: u64 = left.iter()
        .zip(right.iter())
        .map(|(a, b)| if a > b { a - b } else { b - a })
        .sum();
    println!("{}", differences);

    let similarity: u64 = left.iter()
        .map(|a| {
            let occurences = right.iter().filter(|b| a == *b).count();
            a * occurences as u64
        })
        .sum();
    println!("{}", similarity);
}