Exam 4. Activity Tracker

import java.util.Locale;
import java.util.Scanner;
import java.util.TreeMap;

public class _4_ActivityTracker {

    public static void main(String[] args) {
        // TODO Auto-generated method stub
        Locale.setDefault(Locale.ROOT);
        Scanner scan = new Scanner(System.in);
        int count = scan.nextInt();

        TreeMap<Integer, TreeMap<String, Integer>> monthsActivity = new TreeMap<>();
        for (int i = 0; i < count; i++) {
            String dateStr = scan.next();
            String[] splittedString = dateStr.split("/");
            int month = Integer.parseInt(splittedString[1]);
            String userName = scan.next();
            int distance = scan.nextInt();
            scan.nextLine();

            TreeMap<String, Integer> usersActivity;
            if (!monthsActivity.containsKey(month)) {
                usersActivity = new TreeMap<>();
                usersActivity.put(userName, distance);
            } else {
                usersActivity = monthsActivity.get(month);
                Integer previous = usersActivity.get(userName);
                if (previous == null) {
                    previous = 0;
                }

                usersActivity.put(userName, previous + distance);
            }

            monthsActivity.put(month, usersActivity);
        }

        for (Integer month : monthsActivity.keySet()) {
            System.out.print(month + ": ");
            TreeMap<String, Integer> userActivity = monthsActivity.get(month);
            boolean isFirst = true;
            for (String user : userActivity.keySet()) {
                if (!isFirst) {
                    System.out.print(", ");
                }

                isFirst = false;
                System.out.print(user + "(");
                System.out.print(userActivity.get(user) + ")");
            }

            System.out.println();
        }
    }

}