// CSE 373, Winter 2013, Marty Stepp
// A HashIntSet object represents a set of objects using a hash table
// as the internal data structure.
// The hash table uses linear probing to resolve collisions.

import java.util.Arrays;

public class HashSet<E> implements Set<E> {
	private static final Object REMOVED = new Object();
	private Object[] elements;
	private int size;
	
	// Constructs a new empty set of integers.
	public HashSet() {
		elements = new Object[10];
		size = 0;
	}
	
	// Adds the given value to this set,
	// if it was not already contained in the set.
	public void add(E value) {
		if ((double) size / elements.length >= 0.75) {
			rehash();
		}
		
		int h = hash(value);
		while (elements[h] != null && !elements[h].equals(value) &&
				!elements[h].equals(REMOVED)) {
			// collision; "linear probing" to find a spot
			h = (h + 1) % elements.length;
		}
		
		// elements[h] == 0 || elements[h] == value
		if (elements[h] != value) {
			elements[h] = value;
			size++;
		}
	}

	// Returns whether the given value is found in this set.
	public boolean contains(E value) {
		int h = hash(value);
		while (elements[h] != null) {
			if (elements[h].equals(value)) {
				return true;
			}
			// collision; "linear probing" to find a spot
			h = (h + 1) % elements.length;
		}
		
		// found a 0; not here
		return false;
	}

	// Returns true if there are no elements in this set.
	public boolean isEmpty() {
		return size == 0;
	}
	
	// Removes the given element value from this set,
	// if it was found in the set.
	public void remove(E value) {
		int h = hash(value);
		while (elements[h] != null && !elements[h].equals(value)) {
			// collision; "linear probing" to find a spot
			h = (h + 1) % elements.length;
		}
		
		// elements[h] == 0 || elements[h] == value
		if (elements[h] == value) {
			elements[h] = REMOVED;
			size--;
		}
	}

	// Returns the number of elements in this set.
	public int size() {
		return size;
	}
	
	// Returns a text representation of this set.
	// TODO: finish (this is not a proper toString; it shows the internal array)
	public String toString() {
		return Arrays.toString(elements);
	}
	
	
	
	// Debugging helper that prints the inner hash table.
	public void debug() {
		System.out.printf("%7s", "index");
		for (int i = 0; i < elements.length; i++) {
			System.out.printf("%7d", i);
		}
		System.out.println();
		
		System.out.printf("%7s", "value");
		for (int i = 0; i < elements.length; i++) {
			System.out.printf("%7d", elements[i]);
		}
		System.out.println();
		System.out.printf("%7s%7d\n\n", "size", size);
	}
	
	// resize to 2x as big
	@SuppressWarnings("unchecked")
	private void rehash() {
		Object[] big = new Object[2 * elements.length];
		Object[] old = elements;
		size = 0;
		elements = big;
		
		for (Object o : old) {
			if (o != null && o != REMOVED) {
				add((E) o);
			}
		}
	}
	
	// hash function for mapping values to indexes
	private int hash(E value) {
		return Math.abs(value.hashCode()) % elements.length;
	}
}