using System;

using System.Collections.Generic;

using System.Diagnostics;

using System.Linq;

using System.Text;

using System.Threading.Tasks;

​

namespace ConsoleApplication9

{

    public class Program

    {

        public static void Main()

        {

            Stopwatch timer = Stopwatch.StartNew();

            Original();

            timer.Stop();

            Console.WriteLine("Orignal: " + timer.ElapsedTicks);

​

            timer = Stopwatch.StartNew();

            Tommy();

            timer.Stop();

            Console.WriteLine("Tommy: " + timer.ElapsedTicks);

​

            timer = Stopwatch.StartNew();

            berkser();

            timer.Stop();

            Console.WriteLine("Berkser: " + timer.ElapsedTicks);

​

            timer = Stopwatch.StartNew();

            Hari();

            timer.Stop();

            Console.WriteLine("Hari: " + timer.ElapsedTicks);

​

            timer = Stopwatch.StartNew();

            user3185569();

            timer.Stop();

            Console.WriteLine("user3185569: " + timer.ElapsedTicks);

​

            Console.ReadLine();

        }

​

        public static void Original()

        {

            int[] arr = new int[] { 1, 2, 2, 3, 3, 3, 4, 4, 4, 4 };

            var countlist = arr.Aggregate(new Dictionary<int, int>(), (D, i) => {

                D[i] = D.ContainsKey(i) ? (D[i] + 1) : 1;

                return D;

            })

                                .AsQueryable()

                                .OrderByDescending(x => x.Value)

                                .Select(x => x.Key)

                                .ToList();

            // print the element which appears with the second 

            // highest frequency in arr

            Console.WriteLine(countlist[3]); // should print 3

        }

​

        public static void berkser()

        {

​

​

            int[] arr = new int[] { 1, 2, 2, 3, 3, 3, 4, 4, 4, 4 };

​

            var result = arr.GroupBy(x => x)

                            .Select(x => new { Item = x.Key, Count = x.Count() })

                            .OrderBy(x => x.Count);

            Console.WriteLine(result.ElementAt(2).Item);

​

​

        }

​

        public static void Tommy()

        {

            int[] arr = new int[] { 1, 2, 2, 3, 3, 3, 4, 4, 4, 4 };

​

            var lookup = arr.ToLookup(t => t);

            var result = lookup.OrderByDescending(t => t.Count());

​

            Console.WriteLine(result.ElementAt(1).Key);

        }

​

        public static void Hari()

        {

            int[] arr = new int[] { 1, 2, 2, 3, 3, 3, 4, 4, 4, 4 };

​

            int rank = 2;

            var item = arr.GroupBy(x => x)          // Group them

               .OrderByDescending(x => x.Count())   // Sort based on number of occurrences

               .Skip(rank - 1)                      // Traverse to the position

               .FirstOrDefault();                 // Take the element

​

            if (item != null)

            {

                Console.WriteLine(item.Key);

                // output - 3

            }

        }

​

        public static void user3185569()

        {

            int[] arr = new int[] { 1, 2, 2, 3, 3, 3, 4, 4, 4, 4 };

            NthElement4(arr, 3);

        }

​

        private static int? NthElement4(int[] array, int n)

        {

            if (array.Length == 0)

                return null;

​

            int[] holdingResults = new int[array.Max()];

​

            foreach (int i in array)

            {

                holdingResults[i - 1]++;

            }

​

            int? currentMax = new int?();

            int currentMaxIndex = 0;

            for (int i = 0; i < n; i++)

            {

                int localMax = 0;

                int localMaxIndex = 0;

                for (int j = 0; j < holdingResults.Length; j++)

                {

                    int currentItem = holdingResults[j];

​

                    if (currentItem > localMax && (!currentMax.HasValue || currentItem < currentMax))

                    {

                        localMax = currentItem;

                        localMaxIndex = j;

                    }

                }

​

                if (localMax < currentMax || !currentMax.HasValue)

                {

                    currentMax = localMax;

                    currentMaxIndex = localMaxIndex;

                }

            }

​

            return currentMaxIndex + 1;

        }

​

​

    }

}

​