MostFrequentSubstring.cs

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

namespace MostFrequentSubstringApp
{
    /// <summary>
    /// Find the Most Frequent Substring of length between k and l.
    /// 
    /// Input:
    /// n (string length)
    /// k l
    /// teststring 
    /// 
    /// Example (console):
    /// 6
    /// 2 3
    /// ababab
    /// 
    /// Result: ab
    ///
    /// </summary>
    class Program
    {
        static void Main(string[] args)
        {
            var input = GetInputs();
            var k = ToInt(input.ElementAt(1).First());
            var l = ToInt(input.ElementAt(1).ElementAt(1));            
            var s = input.ElementAt(2).First();
            var mostFrequentString = MostFrequentSubstring(s, k, l);

            Console.Write("The most frequent substring is: ");
            Console.WriteLine(mostFrequentString);
        }

        private static IList<IList<string>> GetInputs()
        {
            return Enumerable.Range(0, 3)
                             .Select(x => GetLine())
                             .ToList();
        }

        public static int ToInt(string s)
        {
            int aux = 0;
            int.TryParse(s, out aux);
            return aux;
        }
                
        public static IList<string> GetLine()
        {
            Regex r = new Regex("\\s+", RegexOptions.Compiled);
            var s = Console.ReadLine();
            return r.Split(s).ToList();
        }
                
        public static string MostFrequentSubstring(string s, int k, int l)
        {
            var sortedDict = new Dictionary<string, int>();

            while (k <= l)
            {
                var substrings = Split(s, k); //divide into chunks

                //add or increment
                foreach (var item in substrings)
                {
                    if (sortedDict.ContainsKey(item))
                    {
                        sortedDict[item]++;
                    }
                    else{
                        sortedDict.Add(item, 1);
                    }
                }                
                k++;
            }
            var mostFrequent = sortedDict.OrderByDescending(w => w.Value).FirstOrDefault(); //a sorted dictionary would be better!
            return mostFrequent.Key;
        }

        static IEnumerable<string> Split(string s, int size)
        {
            return Enumerable.Range(0, s.Length / size)
                .Select(i => s.Substring(i * size, size));
        }
    }
}