pick most, C# - rextester

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//Rextester.Program.Main is the entry point for your code. Don't change it.
//Compiler version 4.0.30319.17929 for Microsoft (R) .NET Framework 4.5

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

namespace Rextester
{
    public class Program
    {
        public static void Main(string[] args)
        {
            string text = "xfoofoobarbar fooxxfoo barxxxfoo";
            var allSubstrings = Enumerable.Range(2,text.Length-2)
                .Select(x => {
                        var longestSub = FindSubStrings(text,x).GroupBy(y => y).OrderByDescending(y => y.Count()).FirstOrDefault();
                        return new Substrings {
                            Length = x,
                            Count = longestSub.Count(),
                            Value = longestSub.Key
                        };
                });
            
            foreach(var item in allSubstrings)
            {
                Console.WriteLine(item.Length + ":" + item.Count + ":" + item.Value);
            }
            
            var best = allSubstrings.Where(x => x.Count>1).OrderByDescending(x => x.Length).ThenByDescending(x => x.Count).First();
            
            Console.WriteLine("Longest, most frequest substring is " + best.Value);
        }
        
        public class Substrings
        {
            public int Length{get;set;}
            public int Count{get;set;}
            public string Value{get;set;}
        }
        
        private static IEnumerable<string> FindSubStrings(string input, int length)
        {
            for(var i=0;i<input.Length-length;i++)
            {
                yield return input.Substring(i,length);
            }
        }
                          
                          
    }
}

Show compiler warnings [ + ] Show input
Compilation time: 0,16 sec, absolute running time: 0,11 sec, cpu time: 0,12 sec, average memory usage: 15 Mb, average nr of threads: 3