// This implementation does not work for 
// collisions, but it introduces the idea
// of using hash codes
public class HashStringSet {
   private String[] hashTable;
   private int size;
   
   // Constructs a new, empty set with the given underlying capacity
   public HashStringSet(int capacity) {
      hashTable = new String[capacity];
      size = 0;
   }
   
   private int hashIndex(String element) {
      int index = Math.abs(element.hashCode() % hashTable.length);
      return index;
   }
     
   // Returns true if this set contains the specified element and false otherwise
   public boolean contains(String element) {
      int index = hashIndex(element);
      return hashTable[index] != null;
   }
   
   // Adds the specified element to this set if it is not already present.
   // Returns true if the element was not already present and false otherwise
   public boolean add(String element) {
      if (contains(element)) {
         return false;
      }
      int index = hashIndex(element);
      hashTable[index] = element;
      size++;
      return true;
   }
   
   // Removes the specified element from this set if it is present.
   // Returns true if the element was present and false otherwise
   public boolean remove(String element) {
      if (!contains(element)) {
         return false;
      }
      int index = hashIndex(element);
      hashTable[index] = null;
      size--;
      return true;
   }
   
   // Returns the number of elements in this set
   public int size() {
      return this.size;
   }
   
   // Returns true if this set contains no elements
   public boolean isEmpty() {
      return this.size == 0;
   }
}