616. Add Bold Tag in String

AddBlodTag.cs

public class Solution {
  public string AddBoldTag(string s, string[] words) {
    BitArray FindMatches(){
      var i = 0;
      var bits = new BitArray(s.Length);
      while(i < s.Length){
        foreach(var word in words){
          if(i + word.Length > s.Length)            
            continue;
          var k = i;
          for(var j = 0; j < word.Length; ++j, ++k){
            if(word[j] != s[k])            
              break;
          }
          // i: 6, k: 8
          //Console.WriteLine($"i: {i}, k: {k}, {word}, {k - i == word.Length}");
          if(k - i == word.Length){
            for(int j = i, l = 0; l < word.Length; ++j, ++l)
              bits[j] = true;
          }
        }
        i++;
      }
      return bits;
    }
    var bits = FindMatches();
    var sb = new StringBuilder();
    var i = 0;
    // for(var k = 0; k < bits.Length; k++)
    //   Console.Write($"{(bits[k] ? 1 : 0)}");
    while(i < bits.Length){
      if(bits[i]){
        sb.Append("<b>");
        while(i < bits.Length && bits[i]){
          sb.Append(s[i]);
          i++;
        }
        sb.Append("</b>");
      }
      else{
        sb.Append(s[i]);
        i++;
      }
    }

    return sb.ToString();
  }
}