// CSE 143, Winter 2012
// This class implements a set using a "hash table" array.
// The hash table stores each integer at a particular given index based
// on a "hashing function" represented by the 'bucket' method.
// This provides O(1) average time to add, remove, and search.  (Wow!)

import java.util.*;

public class HashIntSet {
    // "load factor" - percentage of array that must be full before resize
	private static final double LOAD_FACTOR = 0.75;
	
	// "hash table" - an array of hash "buckets" where values can be stored
	private List<Integer>[] elementData;
	private int size;
	
    // Creates a new empty set with a hash table of default capacity of 10.
	public HashIntSet() {
		elementData = (List<Integer>[]) new List[10];
		size = 0;
	}
	
    // Adds the given value to this set.  If it is already contained in
    // this set, no change is made, because sets do not allow duplicates.
	public void add(int value) {
		int h = HF(value);
		if (!contains(value)) {
			if (size >= LOAD_FACTOR * elementData.length) {
				rehash();
			}
			if (elementData[h] == null) {
				elementData[h] = new LinkedList<Integer>();
			}
			elementData[h].add(0, value);
			size++;
		}
	}
	
    // Returns true if the given value is contained in this set, else false.
	public boolean contains(int value) {
		int h = HF(value);
		return elementData[h] != null && 
			   elementData[h].contains(value);
	}
	
	// Returns true if there are no elements in this set.
	public boolean isEmpty() {
		return size() == 0;
	}
	
    // Removes the given value from this set if it is contained in the set.
    // If the value is not contained in the set, no change is made.
	public void remove(int value) {
		if (contains(value)) {
			elementData[HF(value)].remove(value);
			size--;
		}
	}
	
	// Returns the number of elements in this set.
	public int size() {
		return size;
	}
	
	// Returns a string representation of this set for debugging.
	public String toString() {
		return Arrays.toString(elementData);
	}
	
    // Helper method to perform a "hashing function" to map the given value to
    // its appropriate hash table index.
	private int HF(int value) {
		return Math.abs(value) % elementData.length;
	}
	
	// Resizes this set's hash table array to be twice as large.
	// Must re-add all values back into the table because their HF indexes
	// might have changed after the resizing.
	private void rehash() {
		List<Integer>[] oldElementData = elementData;
		elementData = (List<Integer>[]) new List[2 * elementData.length];
		size = 0;
		for (int i = 0; i < oldElementData.length; i++) {
			if (oldElementData[i] != null) {
				for (int value : oldElementData[i]) {
					add(value);
				}
			}
		}
	}
}