// Erika Wolfe, CSE 143
// Hash table implementation of a set, an unordered collection without duplicates.
// The hash table stores values at indexes determined by a hashing function.

// This very basic implementation has no collision resolution so it will only work 
// if all inserted values hash to unique indexes.
public class HashSetIncomplete<E> implements Set<E> {
    private int size;
    private E[] elementData;
    
    public static final int DEFAULT_CAPACITY = 10;
    
    // Constructs an empty set of default capacity
    public HashSetIncomplete() {
        size = 0;
        // this is how you make generic arrays
        elementData = (E[]) new Object[DEFAULT_CAPACITY];
    }
    
    // Adds the given value to the set
    public void add(E val) {
        if (!contains(val)) {
            int index = indexOf(val);
            elementData[index] = val;
            size++;
        }
    }

    // Returns the size of this set
    public int size() {
        return size;
    }

    // Returns true if the set has no elements, false otherwise.
    public boolean isEmpty() {
        return size == 0;
    }

    // Returns whether the given value is in the set
    public boolean contains(E val) {
        int index = indexOf(val);
        return elementData[index] != null;
    }

    // Removes the given value from the set
    // If the set does not contain the given value, the set is unmodified.
    public void remove(E val) {
        if (contains(val)) {
            int index = indexOf(val);
            elementData[index] = null;
            size--;
        }
    }
    
    // Uses the hashing function to find the index of a value.
    private int indexOf(E val) {
        return Math.abs(val.hashCode()) % elementData.length;
    }
}