code: public static int findNthByte(byte [] utf, byte b, int n) {
      return findNthByte(utf, 0, utf.length, b, n);      
    }
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 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