code: protected String findPath(String start, String end) {
          if (start.equals(end)) {
              return start;
          } else {
              return findPath(start, parent.get(end)) + " -> " + end;
          }
      }
docs: Find the path.
  
  @param start key of first node in the path
  @param end key of last node in the path
  @return string containing the nodes keys in the path separated by arrow symbol