ScrabbleCheck.cs

using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Text;

// used in constructing answer at
// https://puzzling.stackexchange.com/questions/100498/how-many-times-can-the-x-tile-be-used-in-one-scrabble-game/100572#100572

public class ScrabbleCheck
{
  static public void Main()
  {
    HashSet<string> ValidWords = new HashSet<string>(ReadFileLines("scrabble.txt").Select(l => l.ToUpperInvariant()));
    Dictionary<string, List<List<string>>> chains = new Dictionary<string, List<List<string>>>();
    foreach (var word in ValidWords.Where(l => l.Contains('X')).OrderBy(l => l.Length))
    {
      int bestChainLength = 0;
      List<List<string>> bestChains = null;
      foreach (var chain in chains)
      {
        if (word.Contains(chain.Key))
        {
          if (chain.Value[0].Count > bestChainLength)
          {
            bestChainLength = chain.Value.Count;
            bestChains = chain.Value.Select(l => new List<string>(l) { word }).ToList();
          }
          else if (chain.Value[0].Count == bestChainLength)
            bestChains.AddRange(chain.Value.Select(l => new List<string>(l) { word }));
        }
      }
      chains.Add(word, bestChains ?? new List<List<string>> { new List<string> { word } });
    }
    foreach (var greatChain in chains.OrderByDescending(chain => chain.Value[0].Count).Take(5))
    {
      foreach(var path in greatChain.Value)
        Console.WriteLine($"{path.Count}: " + string.Join(" => ", path));
    }
    ValidWords.Remove("DI");
    foreach (var word in ValidWords)
    {
      if (word.Length == 7 && !word.Contains('S') &&
         word[0] == 'A' &&
         ValidWords.Contains(word[1] + "I") &&
         ValidWords.Contains(word[2] + "M") &&
         ValidWords.Contains(word[3] + "A") &&
         ValidWords.Contains(word[4] + "L") &&
         ValidWords.Contains(word[5] + "I"))
        Console.WriteLine($"Word above: {word}");
      else if (word.Length == 4 && word[0] == 'E' && word[1] == 'S')
        Console.WriteLine("Word down: " + word);
    }
  }


  public static IEnumerable<string> ReadFileLines(string inputFile)
  {
    using (var file = new StreamReader(inputFile))
    {
      while (!file.EndOfStream)
        yield return file.ReadLine();
    }
  }
}