11.AsociativeArrays-Courses

11. Courses
Write a program that keeps information about courses. Each course has a name and registered students.
You will be receiving a course name and a student name, until you receive the command "end". Check if such course already exists, and if not, add the course. Register the user into the course. When you receive the command "end", print the courses with their names and total registered users, ordered by the count of registered users in descending order. For each contest print the registered users ordered by name in ascending order.
Input
• Until the "end" command is received, you will be receiving input in the format: "{courseName} : {studentName}".
• The product data is always delimited by " : ".
Output
• Print the information about each course in the following the format:
"{courseName}: {registeredStudents}"
• Print the information about each student, in the following the format:
"-- {studentName}"
Examples
Input                                                  Output
Programming Fundamentals : John Smith                  Programming Fundamentals: 2
Programming Fundamentals : Linda Johnson               -- John Smith
JS Core : Will Wilson                                  -- Linda Johnson
Java Advanced : Harrison White                         JS Core: 1
end                                                    -- Will Wilson
                                                       Java Advanced: 1
                                                       -- Harrison White



Algorithms : Jay Moore                                 Python Fundamentals: 3
Programming Basics : Martin Taylor                     -- Andrew Robinson
Python Fundamentals : John Anderson                    -- Clark Lewis
Python Fundamentals : Andrew Robinson                  -- John Anderson
Algorithms : Bob Jackson                               Algorithms: 2
Python Fundamentals : Clark Lewis                      -- Bob Jackson
end                                                    -- Jay Moore
                                                       Programming Basics: 1
                                                       -- Martin Taylor



using System;
using System.Collections.Generic;
using System.Linq;

namespace _11Courses
{
    class Program
    {
        static void Main(string[] args)
        {
            var registered = new Dictionary<string, List<string>>();

            string courseAndStudent;

            while ((courseAndStudent = Console.ReadLine()) != "end")
            {
                var courseSplitted = courseAndStudent.Split(" : ");

                var courseName = courseSplitted[0];
                var studentName = courseSplitted[1];

                if (!registered.ContainsKey(courseName))
                {
                    registered.Add(courseName, new List<string>() { studentName });
                }
                else
                {
                    registered[courseName].Add(studentName);
                }
            }

            foreach (var course in registered.OrderByDescending(x => x.Value.Count))
            {
                Console.WriteLine($"{course.Key}: {course.Value.Count()}");

                foreach (var name in course.Value.OrderBy(x => x))
                {
                    Console.WriteLine($"-- {name}");
                }
            }
        }
    }
}