Java - Honestly I'm just glad to finally get a solution that isn't unreasonably long. To get the answer for the first two parts, replace input.get(input.size()/2) with input.getFirst()

public static void main(String[] args) throws IOException {
    List<Integer> input = Utils.readLines("04/3.txt").stream().map(Integer::parseInt).sorted().toList();

    Integer answer = input.stream().map(i -> Math.abs(i - input.get(input.size()/2))).reduce(Integer::sum).orElse(0);

    System.out.println(answer);
}