001package algs13;
002import stdlib.*;
003import java.util.Iterator;
004import java.util.NoSuchElementException;
005
006
007/**
008 *  The {@code ResizingArrayBag} class represents a bag (or multiset) of
009 *  generic items. It supports insertion and iterating over the
010 *  items in arbitrary order.
011 *  <p>
012 *  This implementation uses a resizing array.
013 *  See {@link LinkedBag} for a version that uses a singly linked list.
014 *  The <em>add</em> operation takes constant amortized time; the
015 *  <em>isEmpty</em>, and <em>size</em> operations
016 *  take constant time. Iteration takes time proportional to the number of items.
017 *  <p>
018 *  For additional documentation, see <a href="https://algs4.cs.princeton.edu/13stacks">Section 1.3</a> of
019 *  <i>Algorithms, 4th Edition</i> by Robert Sedgewick and Kevin Wayne.
020 *
021 *  @author Robert Sedgewick
022 *  @author Kevin Wayne
023 */
024public class ResizingArrayBag<Item> implements Iterable<Item> {
025    // initial capacity of underlying resizing array
026    private static final int INIT_CAPACITY = 8;
027
028    private Item[] a;         // array of items
029    private int n;            // number of elements on bag
030
031    /**
032     * Initializes an empty bag.
033     */
034    @SuppressWarnings("unchecked")
035        public ResizingArrayBag() {
036        a = (Item[]) new Object[INIT_CAPACITY];
037        n = 0;
038    }
039
040    /**
041     * Is this bag empty?
042     * @return true if this bag is empty; false otherwise
043     */
044    public boolean isEmpty() {
045        return n == 0;
046    }
047
048    /**
049     * Returns the number of items in this bag.
050     * @return the number of items in this bag
051     */
052    public int size() {
053        return n;
054    }
055
056    // resize the underlying array holding the elements
057    @SuppressWarnings("unchecked")
058    private void resize(int capacity) {
059        assert capacity >= n;
060                Item[] copy = (Item[]) new Object[capacity];
061        for (int i = 0; i < n; i++)
062            copy[i] = a[i];
063        a = copy;
064    }
065
066    /**
067     * Adds the item to this bag.
068     * @param item the item to add to this bag
069     */
070    public void add(Item item) {
071        if (n == a.length) resize(2*a.length);    // double size of array if necessary
072        a[n++] = item;                            // add item
073    }
074
075
076    /**
077     * Returns an iterator that iterates over the items in the bag in arbitrary order.
078     * @return an iterator that iterates over the items in the bag in arbitrary order
079     */
080    public Iterator<Item> iterator() {
081        return new ArrayIterator();
082    }
083
084    // an iterator, doesn't implement remove() since it's optional
085    private class ArrayIterator implements Iterator<Item> {
086        private int i = 0;
087        public boolean hasNext()  { return i < n;                               }
088        public void remove()      { throw new UnsupportedOperationException();  }
089
090        public Item next() {
091            if (!hasNext()) throw new NoSuchElementException();
092            return a[i++];
093        }
094    }
095
096    /**
097     * Unit tests the {@code ResizingArrayBag} data type.
098     *
099     * @param args the command-line arguments
100     */
101    public static void main(String[] args) {
102        ResizingArrayBag<String> bag = new ResizingArrayBag<String>();
103        bag.add("Hello");
104        bag.add("World");
105        bag.add("how");
106        bag.add("are");
107        bag.add("you");
108
109        for (String s : bag)
110            StdOut.println(s);
111    }
112}