test.cs

// find matches in a list of chunks
public static Dictionary<int, double> FindMatches(List<string> chunks, List<string> keywords, int padding = 500)
{
  // create a dictionary to store the document frequency of each keyword
  Dictionary<string, int> df = new Dictionary<string, int>();

  // create a dictionary to store the results
  Dictionary<int, double> results = new Dictionary<int, double>();

  // create a list to store the trimmed chunks
  List<string> trimmedChunks = new List<string>();

  // loop through the chunks
  for (int i = 0; i < chunks.Count; i++)
  {
    // remove the padding from the first and last chunk
    string chunk = i != 0 ? chunks[i].Substring(padding) : chunks[i];
    chunk = i != chunks.Count - 1 ? chunk.Substring(0, chunk.Length - padding) : chunk;
    trimmedChunks.Add(chunk.ToLower());
  }

  // loop through the trimmed chunks
  foreach (string chunk in trimmedChunks)
  {
    // loop through the keywords
    foreach (string keyword in keywords)
    {
      // count the occurrences of the keyword in the chunk
      int occurrences = chunk.CountSubstring(keyword);
      
      // add the keyword to the document frequency dictionary
      if (!df.ContainsKey(keyword))
      {
        df[keyword] = 0;
      }
      
      // increment the document frequency
      df[keyword] += occurrences;
    }
  }

  // loop through the trimmed chunks
  for (int chunkId = 0; chunkId < trimmedChunks.Count; chunkId++)
  {
    // initialize the points
    double points = 0;

    // loop through the keywords
    foreach (string keyword in keywords)
    {
      // count the occurrences of the keyword in the chunk
      int occurrences = trimmedChunks[chunkId].CountSubstring(keyword);
      
      // calculate the points
      if (df[keyword] > 0)
      {
        // add the points
        points += occurrences / (double)df[keyword];
      }
    }
    // add the points to the results
    results[chunkId] = points;
  }

  // return the results sorted by points
  return results.OrderByDescending(x => x.Value).ToDictionary(x => x.Key, x => x.Value);
}