115 lines
3.3 KiB
Java
115 lines
3.3 KiB
Java
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/*************************************************************************
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* Compilation: javac ResizingArrayBag.java
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* Execution: java ResizingArrayBag
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*
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* Bag implementation with a resizing array.
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*
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*************************************************************************/
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import java.util.Iterator;
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import java.util.NoSuchElementException;
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import edu.princeton.cs.introcs.StdOut;
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/**
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* The ResizingArrayBag class represents a bag (or multiset) of
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* generic items. It supports insertion and iterating over the
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* items in arbitrary order.
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*
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* This implementation uses a resizing array.
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* See {@link LinkedBag} for a version that uses a singly-linked list.
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* The add operation takes constant amortized time; the
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* isEmpty , and size operations
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* take constant time. Iteration takes time proportional to the number of items.
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*
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* For additional documentation, see <a href="http://algs4.cs.princeton.edu/13stacks">Section 1.3</a> of
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* Algorithms, 4th Edition by Robert Sedgewick and Kevin Wayne.
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*
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* @author Robert Sedgewick
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* @author Kevin Wayne
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*/
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public class ResizingArrayBag<Item> implements Iterable<Item> {
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private Item[] a; // array of items
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private int N = 0; // number of elements on stack
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/**
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* Initializes an empty bag.
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*/
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public ResizingArrayBag() {
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a = (Item[]) new Object[2];
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}
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/**
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* Is this bag empty?
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* @return true if this bag is empty; false otherwise
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*/
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public boolean isEmpty() {
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return N == 0;
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}
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/**
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* Returns the number of items in this bag.
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* @return the number of items in this bag
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*/
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public int size() {
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return N;
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}
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// resize the underlying array holding the elements
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private void resize(int capacity) {
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assert capacity >= N;
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Item[] temp = (Item[]) new Object[capacity];
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for (int i = 0; i < N; i++)
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temp[i] = a[i];
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a = temp;
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}
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/**
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* Adds the item to this bag.
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* @param item the item to add to this bag
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*/
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public void add(Item item) {
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if (N == a.length) resize(2*a.length); // double size of array if necessary
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a[N++] = item; // add item
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}
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/**
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* Returns an iterator that iterates over the items in the bag in arbitrary order.
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* @return an iterator that iterates over the items in the bag in arbitrary order
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*/
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public Iterator<Item> iterator() {
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return new ArrayIterator();
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}
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// an iterator, doesn't implement remove() since it's optional
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private class ArrayIterator implements Iterator<Item> {
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private int i = 0;
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public boolean hasNext() { return i < N; }
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public void remove() { throw new UnsupportedOperationException(); }
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public Item next() {
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if (!hasNext()) throw new NoSuchElementException();
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return a[i++];
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}
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}
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/**
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* Unit tests the ResizingArrayBag data type.
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*/
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public static void main(String[] args) {
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ResizingArrayBag<String> bag = new ResizingArrayBag<String>();
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bag.add("Hello");
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bag.add("World");
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bag.add("how");
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bag.add("are");
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bag.add("you");
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for (String s : bag)
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StdOut.println(s);
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}
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}
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