Email everywhere - score 19 maximum score 30

EmailEverywhere_score19.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace Email
{
    class Program
    {
        static void Main(string[] args)
        {
            ProcessInput(); 
            //RunTestcase(); 
        }

        public static void RunTestcase()
        {
            var queries = 3;

            const int MAX = 100000;
            var queueByPriority = new Queue<string>[MAX]; // priority - 1
            int highestPriority = -1;
            for (int i = 0; i < MAX; i++)
            {
                queueByPriority[i] = new Queue<string>();
            }

            var messages = new string[] { "store email1 1", "store email2 10", "get_next_email" };

            IList<string> result = new List<string>(); 

            for (int i = 0; i < queries; i++)
            {
                var command = messages[i].Split(' ');

                if (command.Length == 1)
                {
                    // get next email
                    result.Add( RemoveFirstEmail(queueByPriority, MAX, ref highestPriority));
                }
                else
                {
                    var message = command[1];
                    var priority = command[2];

                    SaveMessageToQueue(queueByPriority, message, priority, ref highestPriority);
                }
            }
        }

        public static void ProcessInput()
        {
            var queries = Convert.ToInt32(Console.ReadLine());

            const int MAX = 100000;
            var queueByPriority = new Queue<string>[MAX]; // priority - 1
            int highestPriority = -1;
            for (int i = 0; i < MAX; i++)
            {
                queueByPriority[i] = new Queue<string>();
            }

            for (int i = 0; i < queries; i++)
            {
                var command = Console.ReadLine().Split(' ');
                if (command.Length == 1)
                {
                    // get next email
                    Console.WriteLine(RemoveFirstEmail(queueByPriority, MAX, ref highestPriority));
                }
                else
                {
                    var message = command[1];
                    var priority = command[2];

                    SaveMessageToQueue(queueByPriority, message, priority, ref highestPriority);
                }
            }
        }

        /// <summary>
        /// save - O(1), easy to find the queue, which queue to save - by priority number
        /// </summary>
        /// <param name="queueByPriority"></param>
        /// <param name="message"></param>
        /// <param name="priority"></param>
        public static void SaveMessageToQueue(Queue<string>[] queueByPriority, string message, string priority, ref int highestPriority)
        {
            int index = Convert.ToInt32(priority); 
            queueByPriority[index - 1].Enqueue(message);

            var newPriority = index - 1;
            if (newPriority > highestPriority)
            {
                highestPriority = newPriority; 
            }
        }

        /// <summary>
        /// size is 100000 - need to do time complexity analysis
        /// it is O(n) algorithm to remove, not efficient
        /// </summary>
        /// <param name="queueByPriority"></param>
        /// <param name="size"></param>
        /// <returns></returns>
        public static string RemoveFirstEmail(Queue<string>[] queueByPriority, int size, ref int highestPriority)
        {
            var message = "-1";

            if(highestPriority < 0 && queueByPriority[highestPriority].Count == 0)
            {
                return message; 
            }

            Queue<string> current = queueByPriority[highestPriority];             
   
            message =  current.Dequeue(); 
            
            if(current.Count == 0)
            {
                FindNextHighestPriority(queueByPriority, ref highestPriority); 
            }

            return message; 
        }

        /// <summary>
        /// 
        /// </summary>
        /// <param name="queueByPriority"></param>
        /// <param name="highestPriority"></param>
        public static void FindNextHighestPriority(Queue<string>[] queueByPriority, ref int highestPriority)
        {
            int start = highestPriority; 

            for(int i = start -1; i >= 0; i--)
            {                
                if (queueByPriority[i].Count == 0)
                {
                    continue; 
                }

                highestPriority = i;  // found the one

                return; 
            }

            highestPriority = -1;   // not found 
            return; 
        }
    }
}