node

Node

class Node { 
     char ch = START;
     List<Node> = List.newArrayList();
     void add (String str) {
          if (str.length() == 0)
               return;
          char chNew = str.charAt(0);
          for (Node n : nodes) {
               if (n.ch == chNew) {
                    n.add (str.substring(1));
                    return;
               }
          Node newNode = new Node();
          newNode.ch = chNew;
          new Node.add(str.substring(1));
          nodes.add(newNode);
     }
     String toRegexp() {
          StringBuilder