/**
 * An interface describing a dictionary of strings.
 * The dictionary cannot contain duplicate strings.
 * 
 * @author Stefan Nilsson
 * @version 2012-12-14
 */
public interface StringDictionary { 
    /**
     * Adds the given string to this table.
     * Returns <code>true</code> if the dictionary
     * did not already contain the given string.
     *
     * Complexity: O(1) expected time.
     */
    public boolean add(String s);

    /**
     * Removes the given string from this dictionary
     * if it is present. Returns <code>true</code> if
     * the dictionay contained the specified element.
     *
     * Complexity: O(1) expected time.
     */
    public boolean remove(String s);

    /**
     * Returns <code>true</code> if the string is
     * in this dictionary.
     *
     * Complexity: O(1) expected time.
     */
    public boolean contains(String s);
 }