// Zorah Fung, 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;

    // Builds a new HashSet of the default capacity
    public HashSetIncomplete() {
        this(DEFAULT_CAPACITY);
    }

    // Builds a new HashSet of the specified capacity
    public HashSetIncomplete(int capacity) {
        elementData = (E[]) new Object[capacity]; // don't worry about this casting
    }

    // Adds the given value to the set
    // Pre: There is nothing at indexOf(value)
    public void add(E value) {
        if (!contains(value)) {
            elementData[indexOf(value)] = value;
            size++;
        }
    }

    // Remove the given value from the set
    public void remove(E value) {
        if (contains(value)) {
            elementData[indexOf(value)] = null;
            size--;
        }
    }

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

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

    // Returns true if this set is empty, false otherwise
    public boolean isEmpty() {
        return size == 0;
    }

    // Returns the String representation of this set.
    public String toString() {
        if (isEmpty()) {
            return "[]";
        } else {
            String result = "[";
            for (int i = 0; i < elementData.length; i++) {
                if (elementData[i] != null) {
                    result += elementData[i] + ", ";
                }
            }
            return result.substring(0, result.length() - 2) + "]";
        }
    }

    // Uses the hashing function to find the index of a value.
    private int indexOf(E value) {
        return Math.abs(value.hashCode() % elementData.length);
    }
}