stupid_file_sort_in_csharp.cs

using System.IO;
using System.Diagnostics;
using static System.Console;
var sw = Stopwatch.StartNew();
var alf = get_alf();
do_it(2_000_000);
sw.Stop();
WriteLine(sw.Elapsed); // <= 00:00:13.4216229 it is very fast! fantasctic!

char[] get_alf()
{
    var list = new List<char>();
    for (char x = 'A'; x <= 'Z'; x++)
        list.Add(x);
    for (char x = 'a'; x <= 'z'; x++)
        list.Add(x);
    list.Add(' ');

    return list.ToArray();
}

string gen_str()
{
    var range = Enumerable.Range(0, Random.Shared.Next(20, 100));
    var chars = range.Select(x => alf[Random.Shared.Next(0, alf.Length)]).ToArray();
    return new string(chars);
}

int gen_num() => Random.Shared.Next(0, 10_000);

void do_it(int count)
{

    var source = $"L{count}.txt";
    var dist = $"S{count}.txt";
    var comp = new SimpleComparer();
    File.WriteAllLines(source, Enumerable.Range(0, count).Select(x => $"{gen_num()}.{gen_str()}"));
    File.WriteAllLines(dist, File.ReadAllLines(source).OrderBy(x => x, comp));
}

class SimpleComparer : IComparer<string>
{
    public int Compare(string s1, string s2)
    {
        var p1 = s1.IndexOf('.');
        var v1 = s1.AsSpan(p1 + 2);

        var p2 = s2.IndexOf('.');
        var v2 = s2.AsSpan(p2 + 2);

        var vc =
            v1.CompareTo(v2, StringComparison.Ordinal);

        if (vc != 0)
            return vc;
        else
        {
            var n1 = Int32.Parse(s1.AsSpan(0, p1));
            var n2 = Int32.Parse(s2.AsSpan(0, p2));
            return n1.CompareTo(n2);
        }
    }
}