Courses [Mimi]

import java.util.*;

public class _06_Courses {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);

        Map<String, List<String>> courseByStudents = new LinkedHashMap<>();

        String input = "";
        while (!"end".equals(input = scanner.nextLine())) {
            String[] line = input.split(" : ");

            courseByStudents.putIfAbsent(line[0], new ArrayList<>());
            courseByStudents.get(line[0]).add(line[1]);
            Collections.sort(courseByStudents.get(line[0]));
        }

        courseByStudents
                .entrySet()
                .stream()
                .sorted((x, y) -> Integer.compare(y.getValue().size(), x.getValue().size()))
                .forEach(entry -> {
                    System.out.println(String.format("%s: %d", entry.getKey(), entry.getValue().size()));
                    entry.getValue().forEach(e -> {
                        System.out.println("-- " + e);
                    });
                });
    }
}