Courses Maps

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.*;

public class Courses {
    public static void main(String[] args) throws IOException {
        BufferedReader read = new BufferedReader(new InputStreamReader(System.in));
        Map<String, List<String>> courses = new LinkedHashMap<>();
        String command;
        while (!"end".equals(command = read.readLine())) {

            String[] info = command.split(" : ");

            courses.putIfAbsent(info[0], new ArrayList<>());
            courses.get(info[0]).add(info[1]);

        }
        courses.entrySet().stream().sorted((course, num) -> Integer.compare(num.getValue().size(), course.getValue().size())).forEach(entry -> {
            System.out.println(String.format("%s: %d", entry.getKey(), entry.getValue().size()));
            Collections.sort(entry.getValue());
            entry.getValue().forEach(name -> System.out.println("-- " + name));
        });
    }
}