public class PrefixTree {
    private PTNode root;
    private int size;
    
    //constructor
    public PrefixTree ( ) {
    	root = new PTNode ("");
	}
    
    public PTNode getRoot ( ) {
    	return root;
    }
    
    public void setRoot (PTNode node) {
    	root = node;
	}
    
    public int getSize ( ) {
    	return size;
    }
    
    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) {
    // add new nodes to calling tree, for w and any of its prefixes that are new
    	PTNode current = root;
    	for (int i = 0; i < w.length( ); i++) {
            //if not a letter, break because of illegal input
    		if ((w.charAt(i) < 'a') || (w.charAt(i) > 'z')) 
            	break;
    		//otherwise, check if there is already a node with the next letter
            if (current.getChild (w.charAt(i)) == null){ //if not, add a new node
	            current.setChild(w.charAt(i), w.substring(0, i+1));
	            //remember to increment size
	            if(w.substring(i).length() == 1) size++;
            }
            // else a child node already exists, so just traverse down
            current = current.getChild(w.charAt(i));
        }
    }
}