//Thank you for watching my video private static void mergesort(string[] a, int first, int last) { if (first < last) { //Safe way to avoid overflowing. (first + last)/2 can overflow int last_first = last - first; int middle = first + last_first/2; //To minimize dividing, we use insertion sort on subarrays have // sizes less than 16. Subarray size is actually last - first +1. // It is ok to use last - first only to save + 1 operation. if (last_first < 16) { //The below is inline insertion sort int endi=last +1; int endj=first - 1; string current; int j; int i = first + 1; while (i < endi) { current = a[i]; j = i - 1; while (j > endj && string.CompareOrdinal(a[j], current) > 0) { a[j + 1] = a[j]; j = j - 1; } a[j + 1] = current; i++; } //End inline insertion sort return; } mergesort(a, first, middle); mergesort(a, middle + 1, last); merge(a, first, middle, last); } } private static void merge(string[] a, int first, int mid, int last) { int j, k; int temp_size = last - first + 1; string[] temp = new string[temp_size]; int i = 0; j = first; k = mid + 1; while ((j <= mid) && (k <= last)) { //To sort DESCENDING, we can change < to > if (string.CompareOrdinal(a[j], a[k] ) < 0) { temp[i] = a[j]; j++; } else { temp[i] = a[k]; k++; } i++; } //Optimization here: we copy the left over of the left subarray to //a at the index (first + i). Normally, there is a while loop on j to copy the left over to temp. Then copy temp back to a. So // it repeats copying the left over of the left subarray if (j <= mid) { new Span<string>(a, j, mid - j + 1).CopyTo(new Span<string>(a, first + i, mid - j + 1)); } //Optimization for the left over of the right subarray if(k <= last) { new Span<string>(a, k, last - k + 1).CopyTo(new Span<string>(a, first + i, last - k + 1)); } //Now we copy only i elements back to a //That's why we make a span from 0 and has i elements only temp.AsSpan(0, i).CopyTo(new Span<string>(a, first, i)); } private static bool VerifyOrder(string[] test) { int last = test.Length - 1; bool result= false; int cmp= 0; for (int u = 1; u <= last; u++) { cmp = string.CompareOrdinal(test[u - 1], test[u] ); // The previous element is bigger than the element right after it, so // the sorting is not in ascending order. We break for-loop immediately. //To verify if the array is in DESCENDING order, use cmp < 0 if (cmp > 0) { break; } } //To verify if the array in DESCENDING order, use cmp >=0 if (cmp <= 0) result = true; //test is in ascending order, so return true return result; } //Comparing two sorted string arrays //In the Main(), it should be called as: same(args[0], args[1]) public static bool same(string file1, string file2) { bool result = true; using (StreamReader m = new StreamReader(file1), d = new StreamReader(file2)) { string str1, str2; while ((str1 = m.ReadLine()) != null && (str2 = d.ReadLine()) != null) { if (str1.Equals(str2, StringComparison.OrdinalIgnoreCase) == false) { result = false; break; } } } return result; } //The folling is DotNet() in the video private static void Dotnet() { Console.WriteLine(""); Console.Write("Using DotNet's List's Sort method. Enter input file: "); string filename = Console.ReadLine(); List<string> words = new List<string>(); using (StreamReader st = new StreamReader(filename)) { string aline; aline = st.ReadLine(); while (aline != null) { words.Add(aline); aline = st.ReadLine(); }; } //To sort DESCENDING, we can negate the return: //Comparison<string> cmp = (str1, str2) => -string.CompareOrdinal(str1, str2); Comparison<string> cmp = (str1, str2) => string.CompareOrdinal(str1, str2); Console.WriteLine("Start..."); Stopwatch sw = Stopwatch.StartNew(); words.Sort(cmp); sw.Stop(); string time = sw.Elapsed.TotalMinutes.ToString(); Console.WriteLine("Dotnet List's Sort() Method: " + time + " minutes."); Console.WriteLine("Writing the sorted to file named: DotnetResult"); using (StreamWriter ws = new StreamWriter("DotnetResult")) { foreach (String str in words) { ws.WriteLine(str); } } } // MyMergeSort() is exactly like in the Video

Thank you for uploading code. Can you upload all the code . . . the imports of packages etc.

The above functions are C# code only. I'm using Visual Studio 2019 Community Edition. After creating a C# Console Application Project, there is a file Program.cs which has a class Program and Main() function. The functions in the first reply can be put in the class Program. The using are using System; using System.Collections; using System.Collections.Concurrent; using System.Collections.Generic; using System.Diagnostics; using System.IO; using System.Net; using System.Text; using System.Threading; using System.Threading.Tasks; In the \bin folder of the project, there is \debug or elease. If debug-compiling, the input file to sort has to be in the child folder of the \debug. If release-compiling, the input file to sort has to be in the child folder of the elease. Also there is a *.exe in the child folder. After compling ok, we can close Visual Studio. Running the *.exe file in the child folder gives faster sorting time than running with the Visual Studio. Thank you for watching my video.