Equivalent to matcher.start and matcher.end in C #

I am new to C # and am trying to convert below code to C # but cannot find api in C # to do this.

• Please explain the equivalent of matcher.start () and matcher.end ().

• which is equivalent to matcher.group () in C #.

  private String getFinalVariant(String strInputWord) {
  
  Pattern pat = Pattern.compile("[aeiouhy]+");
  Matcher mat = pat.matcher(strInputWord);
  int lenghtOfInputWord = strInputWord.length();
  while (mat.find()) {
      if (mat.start() == 0) {
  
          int index = '1';
          Map<String, String> temp = ruleList[index];
          if (temp.containsKey(mat.group())) {
              strInputWord = strInputWord.replaceFirst(mat.group(), temp.get(mat.group()));
          }
  
      } else if (mat.end()== lenghtOfInputWord) {
  
          int index = '3';
          int lastIndex = strInputWord.lastIndexOf(mat.group());
          Map<String, String> temp = ruleList[index];
          if (temp.containsKey(mat.group())) {
              String tail = strInputWord.substring(lastIndex).replaceFirst(mat.group(), temp.get(mat.group()));
              strInputWord = strInputWord.substring(0, lastIndex) + tail;
          }
  
      } else {
  
          int index = '2';
          Map<String, String> temp = ruleList[index];
          String str = mat.group();
          // System.out.println(str);
          //  System.out.println(mat.start());
          if (temp.containsKey(mat.group())) {
              if (strInputWord.length() > 3) {
                  int index1 = strInputWord.indexOf(mat.group(), 1);
                  if (index1 != 0 && index1 != strInputWord.length() - 1) {
                      String matched = strInputWord.substring(index1, strInputWord.length() - 1).replaceFirst(mat.group(), temp.get(mat.group()));
                      strInputWord = strInputWord.substring(0, index1) + matched + strInputWord.charAt(strInputWord.length() - 1);
                  }
  
              } else if (strInputWord.length() == 3) {
                  strInputWord = strInputWord.charAt(0) + strInputWord.substring(1, 2).replaceFirst(mat.group(), temp.get(mat.group())) + strInputWord.charAt(strInputWord.length() - 1);
              }
  
          }
  
      }
  
  }
  return strInputWord;
  }