package edu.princeton.cs.algs4.ch13;
import edu.princeton.cs.introcs.*;
/*************************************************************************
* Compilation: javac ResizingArrayStack.java
* Execution: java ResizingArrayStack < input.txt
* Data files: http://algs4.cs.princeton.edu/13stacks/tobe.txt
*
* Stack implementation with a resizing array.
*
* % more tobe.txt
* to be or not to - be - - that - - - is
*
* % java ResizingArrayStack < tobe.txt
* to be not that or be (2 left on stack)
*
*************************************************************************/
import java.util.Iterator;
import java.util.NoSuchElementException;
/**
* The <tt>ResizingArrayStack</tt> class represents a last-in-first-out (LIFO) stack
* of generic items.
* It supports the usual <em>push</em> and <em>pop</em> operations, along with methods
* for peeking at the top item, testing if the stack is empty, and iterating through
* the items in LIFO order.
* <p>
* This implementation uses a resizing array, which double the underlying array
* when it is full and halves the underlying array when it is one-quarter full.
* The <em>push</em> and <em>pop</em> operations take constant amortized time.
* The <em>size</em>, <em>peek</em>, and <em>is-empty</em> operations takes
* constant time in the worst case.
* <p>
* For additional documentation, see <a href="/algs4/13stacks">Section 1.3</a> of
* <i>Algorithms, 4th Edition</i> by Robert Sedgewick and Kevin Wayne.
*
* @author Robert Sedgewick
* @author Kevin Wayne
*/
public class ResizingArrayStack<Item> implements Iterable<Item> {
private Item[] a; // array of items
private int N; // number of elements on stack
/**
* Initializes an empty stack.
*/
public ResizingArrayStack() {
a = (Item[]) new Object[2];
}
/**
* Is this stack empty?
* @return true if this stack is empty; false otherwise
*/
public boolean isEmpty() {
return N == 0;
}
/**
* Returns the number of items in the stack.
* @return the number of items in the stack
*/
public int size() {
return N;
}
// resize the underlying array holding the elements
private void resize(int capacity) {
assert capacity >= N;
Item[] temp = (Item[]) new Object[capacity];
for (int i = 0; i < N; i++) {
temp[i] = a[i];
}
a = temp;
}
/**
* Adds the item to this stack.
* @param item the item to add
*/
public void push(Item item) {
if (N == a.length) resize(2*a.length); // double size of array if necessary
a[N++] = item; // add item
}
/**
* Removes and returns the item most recently added to this stack.
* @return the item most recently added
* @throws java.util.NoSuchElementException if this stack is empty
*/
public Item pop() {
if (isEmpty()) throw new NoSuchElementException("Stack underflow");
Item item = a[N-1];
a[N-1] = null; // to avoid loitering
N--;
// shrink size of array if necessary
if (N > 0 && N == a.length/4) resize(a.length/2);
return item;
}
/**
* Returns (but does not remove) the item most recently added to this stack.
* @return the item most recently added to this stack
* @throws java.util.NoSuchElementException if this stack is empty
*/
public Item peek() {
if (isEmpty()) throw new NoSuchElementException("Stack underflow");
return a[N-1];
}
/**
* Returns an iterator to this stack that iterates through the items in LIFO order.
* @return an iterator to this stack that iterates through the items in LIFO order.
*/
public Iterator<Item> iterator() {
return new ReverseArrayIterator();
}
// an iterator, doesn't implement remove() since it's optional
private class ReverseArrayIterator implements Iterator<Item> {
private int i;
public ReverseArrayIterator() {
i = N-1;
}
public boolean hasNext() {
return i >= 0;
}
public void remove() {
throw new UnsupportedOperationException();
}
public Item next() {
if (!hasNext()) throw new NoSuchElementException();
return a[i--];
}
}
/**
* Unit tests the <tt>Stack</tt> data type.
*/
public static void main(String[] args) {
ResizingArrayStack<String> s = new ResizingArrayStack<String>();
while (!StdIn.isEmpty()) {
String item = StdIn.readString();
if (!item.equals("-")) s.push(item);
else if (!s.isEmpty()) StdOut.print(s.pop() + " ");
}
StdOut.println("(" + s.size() + " left on stack)");
}
}
/*************************************************************************
* Copyright 2002-2012, Robert Sedgewick and Kevin Wayne.
*
* This file is part of algs4-package.jar, which accompanies the textbook
*
* Algorithms, 4th edition by Robert Sedgewick and Kevin Wayne,
* Addison-Wesley Professional, 2011, ISBN 0-321-57351-X.
* http://algs4.cs.princeton.edu
*
*
* algs4-package.jar is free software: you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation, either version 3 of the License, or
* (at your option) any later version.
*
* algs4-package.jar is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
* You should have received a copy of the GNU General Public License
* along with algs4-package.jar. If not, see http://www.gnu.org/licenses.
*************************************************************************/