using System;

using System.Collections.Generic;

using System.Linq;

using System.Diagnostics; 

public static class Program

{

     public static int loopcnt = 0; 

     public static IEnumerable<T> RemoveRange<T>(this IEnumerable<T> source, IEnumerable<T> second)

     {

         var tempList = source.ToList();

​

         foreach (var item in second)

         {

             tempList.Remove(item); //this is cause a copy like RemoveAt below

         }

​

         return tempList;

     }

​

    //RemoveAt for arrays, this is problematic copy and shrink time consuming - see my next post on how to fix this!

    public static void RemoveAt<T>(ref T[] arr, int index)

    {

        for (int a = index; a < arr.Length - 1; a++)

        {

            // moving elements downwards, to fill the gap at [index]

            arr[a] = arr[a + 1];

            loopcnt++; //not required but here for time anaylsis

        }

        // finally, let's decrement Array's size by one

        Array.Resize(ref arr, arr.Length - 1);

    }

    //CHALLENGE - Get difference between two unorderd, not unique lists, duplicates allowed within a list and across both lists.

    //Will demonstrate all solutions from https://stackoverflow.com/questions/15801655/difference-between-two-lists-preserving-duplicates 

    //are WRONG!

    //SOLUTION - https://metadataconsulting.blogspot.com/2021/02/CSharp-dotNet-Get-difference-between-two-unordered-not-unique-lists-aka-duplicates-allowed-within-a-list-and-across-both-lists.html

    //OPTIMIZE - Next blog post will drastically reduce increase the speed of this

    public static void Main()

    {

            Console.WriteLine("Get difference between two unordered, not unique (duplicates) lists!");

            Console.WriteLine("Solution by https://metadataconsulting.blogspot.com/2021/02/CSharp-dotNet-Get-difference-between-two-unordered-not-unique-lists-aka-duplicates-allowed-within-a-list-and-across-both-lists.html");

            Console.WriteLine();

            Stopwatch sw = new Stopwatch();

            sw.Start(); 

​

            //UNORDERED, NOT UNIQUE lists, lists with duplicates 

            string[] arrA = new string[] { "1", "1", "2", "3", "4", "5", "9", "7", "7", "7" };

            string[] arrB = new string[] { "1", "1", "2", "2", "3", "4", "5", "5", "5", "5" };

​

            //DESIRED RESULT = 2,5,5,5,7,7,7,9 OR 2,5,5,5,9,7,7,7 OR 9,7,7,7,2,5,5,5 UNORDERED IS SUFFICIENT, WE LOOKING FOR SPEED

            sw.Stop();

            Console.WriteLine("A  = " + string.Join(",", arrA));

            Console.WriteLine("B  = " + string.Join(",", arrB));

            Console.WriteLine("A Count  = " + arrA.Length);    

            Console.WriteLine("B Count  = " + arrB.Length);

            Console.WriteLine();

            sw.Restart();

​

            //MY IMPLEMENTATION PURE ARRAY SOLUTION -     

            string[] diff = new string[arrA.Length+arrB.Length]; //contains B-A 

            int d = 0; //index for diff list

            bool nf = true; //not found 

            loopcnt = 0; 

            int a = 0;  

            for (int b = 0; b < arrB.Length; b++)

            {

                nf = true;

​

                for (a = 0; a < arrA.Length; a++)

                {

                    if (arrA[a] == arrB[b])

                    {

                        nf = false;

​

                        RemoveAt(ref arrA, a); //magic - removes instance found, A is left with differences not found in B, mathematically A-B = diffsA 

​

                        break;

​

                    }

                }

​

                if (nf) //not found in set B 

                {

                    diff[d] = arrB[b]; //diffs B not found in A, mathematically B-A = diffsB (order important here, driven by B, so those results appear)

                    d++;

                }

                loopcnt++; //not required but here for time anaylsis

            }

            sw.Stop(); 

            Console.WriteLine("No. of loops = " + loopcnt);

            Console.WriteLine("(A-B) Result = " + string.Join(",", arrA).TrimEnd(','));

            Console.WriteLine("(B-A) Result = " + string.Join(",", diff).TrimEnd(','));

            Console.WriteLine("Result Unorderd Final = " + (string.Join(",", diff)).TrimEnd(',') + "," + string.Join(",", arrA) + " in " + sw.ElapsedTicks + " ticks.");

​

            List<string> C = diff.ToList();

​

            List<string> D = diff.ToList().Concat(arrA.ToList()).ToList();

            D.Sort();

​

            Console.WriteLine("Result  Ordered Final = " + string.Join(",", D).TrimStart(','));

            sw.Reset();

            sw.Start();

            Console.WriteLine(); 

            Console.WriteLine("000 StackOverflow answers all wrong 000");

            Console.WriteLine("https://stackoverflow.com/questions/15801655/difference-between-two-lists-preserving-duplicates"); 

            Console.WriteLine("000 I don't post on StackOverflow because of the idiotic moderators and comments 000");

            Console.WriteLine(); 

​

            //https://stackoverflow.com/questions/15801655/difference-between-two-lists-preserving-duplicates

            //Dustin Kingen

            List<string> M = new List<string>() { "1", "1", "2", "3", "4", "5", "9", "7", "7", "7" };

            List<string> N = new List<string>() { "1", "1", "2", "2", "3", "4", "5", "5", "5", "5" };

            var ListDiffs = M.RemoveRange(N);

            sw.Stop();  

            Console.WriteLine("RemoveRage Result = " + string.Join(",", ListDiffs) + " in " + sw.ElapsedTicks + " ticks.");

​

            sw.Reset();

            sw.Start();

            //https://stackoverflow.com/questions/15801655/difference-between-two-lists-preserving-duplicates

            //Ani

            List<string> list2 = new List<string>() { "1", "1", "2", "3", "4", "5", "9", "7", "7", "7" };

            List<string> list1 = new List<string>() { "1", "1", "2", "2", "3", "4", "5", "5", "5", "5" };

            var lookup2 = list2.ToLookup(str => str);

​

            var result = from str in list1

                         group str by str into strGroup

                         let missingCount

                              = Math.Max(0, strGroup.Count() - lookup2[strGroup.Key].Count())

                         from missingStr in strGroup.Take(missingCount)

                         select missingStr;

            sw.Stop();

            Console.WriteLine("Lookup Result = " + string.Join(",", result) + " in " + sw.ElapsedTicks + " ticks.");

            sw.Reset();

            sw.Start();

            List<string> AA = new List<string>() { "1", "1", "2", "3", "4", "5", "9", "7", "7", "7" };

            List<string> BB = new List<string>() { "1", "1", "2", "2", "3", "4", "5", "5", "5", "5" };

            //https://stackoverflow.com/questions/15801655/difference-between-two-lists-preserving-duplicates

            //Sergey Kalinichenko 

            var diffLinq = AA.Select(e => new { Key = e, Val = 1 })

                    .Concat(BB.Select(e => new { Key = e, Val = -1 }))

                    .GroupBy(e => e.Key, e => e.Val)

                    .SelectMany(g => Enumerable.Repeat(g.Key, Math.Max(0, g.Sum())))

                    .ToList();

​

            sw.Stop();

            Console.WriteLine("diffLinq Result = " + string.Join(",", diffLinq) + " in " + sw.ElapsedTicks + " ticks.");

​

​

​

​

    }

}