code: public static int findNthByte(byte [] utf, int start, int length, byte b, int n) {
      int pos = -1;
      int nextStart = start;
      for (int i = 0; i < n; i++) {
        pos = findByte(utf, nextStart, length, b);
        if (pos < 0) {
          return pos;
        }
        nextStart = pos + 1;
      }
      return pos;      
    }
docs: Find the nth occurrence of the given byte b in a UTF-8 encoded string
  @param utf a byte array containing a UTF-8 encoded string
  @param start starting offset
  @param length the length of byte array
  @param b the byte to find
  @param n the desired occurrence of the given byte
  @return position that nth occurrence of the given byte if exists; otherwise -1