using System;

using System.Diagnostics;

using System.Threading;

using System.Threading.Tasks;

​

namespace GenshinOddsSim

{

  class Program

  {

    // Out of 1000ths, not 100ths/percent

    const int _Odds5 = 6;

    const int _OddsFeatured = 3;

​

    enum PullResult

    {

      Miss = 0,

      OffBanner5 = 1,

      Featured5 = 2,

    }

​

    static PullResult Pull(Random rng)

    {

      // If you're not familiar with C# Random(), it rolls inclusive of the min but exclusive of the max. So the below rolls from 0 to 999.

      var result = rng.Next(0, 1000);

​

      // if you roll 6 or greater, its a miss. Otherwise if you roll 3 or greater (3, 4, 5), its an off banner. Anything else (0, 1, 2) is the banner drop.

      return result >= _Odds5 ? PullResult.Miss : result >= _OddsFeatured ? PullResult.OffBanner5 : PullResult.Featured5;

    }

​

    static PullResult PullWithPity(Random rng, int pullCount)

    {

      // 90th pull is a 5 guaranteed.

      if (pullCount % 90 == 0 )

      {

        return rng.Next(0, 2) > 0 ? PullResult.OffBanner5 : PullResult.Featured5;

      }

​

      return Pull(rng);

    }

​

    // Returns pulls needed to get featured

    static int PullsTillFeatured(Random rng)

    {

      int pullCount = 0;

      int pullsSinceLast5 = 0;

​

      PullResult result = PullResult.Miss;

      bool first5 = false;

​

      while (result != PullResult.Featured5)

      {

        ++pullCount;

        ++pullsSinceLast5;

​

        result = PullWithPity(rng, pullsSinceLast5);

        if ( result == PullResult.OffBanner5)

        {

          pullsSinceLast5 = 0;

          if (first5)

          {

            result = PullResult.Featured5;

          }

          else

          {

            first5 = true;

          }

        }

      }

​

      return pullCount;

    }

​

    static Int64 SimPullsTillFeatured5(int totalSims)

    {

      Int64 pullsPerSim = 0;

​

      Random rng = new Random();

      int simCount = 0;

      for (simCount = 0; simCount < totalSims; ++simCount)

      {

        pullsPerSim += PullsTillFeatured(rng);

      }

​

      return pullsPerSim;

    }

​

    static void Main(string[] args)

    {

      // Spoiler : oneBillion sims results in an average of 104,542847234 pulls till Featured

​

      Stopwatch stopWatch = new Stopwatch();

      stopWatch.Start();

​

      const int oneHundredThousand = 100000;

      const int oneMillion = oneHundredThousand * 10;

      const int oneHundredMillion = oneMillion * 100;

      const int oneBillion = oneHundredMillion * 10;

​

      const int targetSims = oneMillion;

      const int simsPerRun = oneHundredThousand;

​

      const int workSplit = targetSims/ simsPerRun;

      int totalSimsRun = 0;

​

      long totalPulls = 0;

      Parallel.For(0, workSplit,

                   index => {

                     var simResult = SimPullsTillFeatured5(simsPerRun);

                     Interlocked.Add(ref totalSimsRun, simsPerRun);

                     Interlocked.Add(ref totalPulls, simResult);

​

                     System.Console.WriteLine($"loop = {index}, sim={simResult}, total={totalPulls}");

                   });

      stopWatch.Stop();

​

      double ave = (double)totalPulls / totalSimsRun;

      System.Console.WriteLine($"\n\tAverage pulls till Featured Character := {ave}\n");

​

      TimeSpan ts = stopWatch.Elapsed;

      Console.WriteLine($"Seconds to complete {ts.TotalSeconds}");

    }

  }

}

​