Efficient .NET dirty word filtering algorithm and application examples

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Collections;
using System.Data;
namespace WNF
{
  public class BadWordsFilter
  {
    private HashSet<string> hash = new HashSet<string>(); //关键字
    private byte[] fastCheck = new byte[char.MaxValue];
    private byte[] fastLength = new byte[char.MaxValue];
    private BitArray charCheck = new BitArray(char.MaxValue);
    private BitArray endCheck = new BitArray(char.MaxValue);
    private int maxWordLength = 0;
    private int minWordLength = int.MaxValue;
    public BadWordsFilter()
    {
    }
    //初始化关键字
    public void Init(DataTable badwords)
    {
      for (int j = 0; j < badwords.Rows.Count; j++)
      {
        string word = badwords.Rows[j][0].ToString();
        maxWordLength = Math.Max(maxWordLength, word.Length);
        minWordLength = Math.Min(minWordLength, word.Length);
        for (int i = 0; i < 7 && i < word.Length; i++)
        {
          fastCheck[word[i]] |= (byte)(1 << i);
        }
        for (int i = 7; i < word.Length; i++)
        {
          fastCheck[word[i]] |= 0x80;
        }
        if (word.Length == 1)
        {
          charCheck[word[0]] = true;
        }
        else
        {
          fastLength[word[0]] |= (byte)(1 << (Math.Min(7, word.Length - 2)));
          endCheck[word[word.Length - 1]] = true;
          hash.Add(word);
        }
      }
    }
    public string Filter(string text, string mask)
    {
      throw new NotImplementedException();
    }
    //检查是否有关键字
    public bool HasBadWord(string text)
    {
      int index = 0;
      while (index < text.Length)
      {
        int count = 1;
        if (index > 0 || (fastCheck[text[index]] & 1) == 0)
        {
          while (index < text.Length - 1 && (fastCheck[text[++index]] & 1) == 0) ;
        }
        char begin = text[index];
        if (minWordLength == 1 && charCheck[begin])
        {
          return true;
        }
        for (int j = 1; j <= Math.Min(maxWordLength, text.Length - index - 1); j++)
        {
          char current = text[index + j];
          if ((fastCheck[current] & 1) == 0)
          {
            ++count;
          }
          if ((fastCheck[current] & (1 << Math.Min(j, 7))) == 0)
          {
            break;
          }
          if (j + 1 >= minWordLength)
          {
            if ((fastLength[begin] & (1 << Math.Min(j - 1, 7))) > 0 && endCheck[current])
            {
              string sub = text.Substring(index, j + 1);
              if (hash.Contains(sub))
              {
                return true;
              }
            }
          }
        }
        index += count;
      }
      return false;
    }
  }
}

string sql = "select keywords from tb_keyword";
BadWordsFilter badwordfilter = new BadWordsFilter();
//初始化关键字
badwordfilter.Init(oEtb.GetDataSet(sql).Tables[0]);
//检查是否有存在关键字
bool a = badwordfilter.HasBadWord(TextBox1.Text);
if (a == true)
{
    Page.RegisterClientScriptBlock("a", "<script>alert(&#39;该评论含有不合法文字！&#39;)</script>");
}
else
{
    PingLun();//写入评论表
}