public class PrefixTree {
    private PTNode root;
    private int size;  // should be number of leaves
    public PTNode getRoot ( ) {return root;}
    public void setRoot (PTNode node) {root = node;}
    public int getSize ( ) {return size;}
    public PrefixTree ( ) {root = new PTNode (""); size = 0;}
    
    public boolean contains (String w) {
    // returns true if calling tree contains a node for the string w
    // this means that the path of w's letters leads to a node,
    // rather than anything to do with the "elem" fields of the nodes
    // assumes that w is a string of lower-case letters, else returns false
        PTNode current = root;
        for (int i = 0; i < w.length( ); i++) {
            if ((w.charAt(i) < 'a') || (w.charAt(i) > 'z')) return false;
            if (current.getChild (w.charAt(i)) == null) return false;
            current = current.getChild (w.charAt(i));}
        return true;}


    public void addString (String w) { // stub, to be written by student
    // add new nodes to calling tree, for w and any of its prefixes that are new
    // should update "size" to add _one_ for the new leaf   
 }}