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/******************************************************************************
* Compilation: javac ResizingArrayStack.java
* Execution: java ResizingArrayStack < input.txt
* Dependencies: StdIn.java StdOut.java
* Data files: https://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)
*
******************************************************************************/
package edu.princeton.cs.algs4;
import java.util.Iterator;
import java.util.NoSuchElementException;
/**
* The {@code ResizingArrayStack} class represents a last-in-first-out (LIFO) stack
* of generic items.
* It supports the usual push and pop operations, along with methods
* for peeking at the top item, testing if the stack is empty, and iterating through
* the items in LIFO order.
*
* 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 push and pop operations take constant amortized time.
* The size, peek, and is-empty operations takes
* constant time in the worst case.
*
* For additional documentation,
* see Section 1.3 of
* Algorithms, 4th Edition by Robert Sedgewick and Kevin Wayne.
*
* @author Robert Sedgewick
* @author Kevin Wayne
*/
public class ResizingArrayStack- implements Iterable
- {
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];
n = 0;
}
/**
* 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;
// textbook implementation
Item[] temp = (Item[]) new Object[capacity];
for (int i = 0; i < n; i++) {
temp[i] = a[i];
}
a = temp;
// alternative implementation
// a = java.util.Arrays.copyOf(a, capacity);
}
/**
* 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
- iterator() {
return new ReverseArrayIterator();
}
// an iterator, doesn't implement remove() since it's optional
private class ReverseArrayIterator implements Iterator
- {
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 {@code Stack} data type.
*
* @param args the command-line arguments
*/
public static void main(String[] args) {
ResizingArrayStack
stack = new ResizingArrayStack();
while (!StdIn.isEmpty()) {
String item = StdIn.readString();
if (!item.equals("-")) stack.push(item);
else if (!stack.isEmpty()) StdOut.print(stack.pop() + " ");
}
StdOut.println("(" + stack.size() + " left on stack)");
}
}
/******************************************************************************
* Copyright 2002-2018, Robert Sedgewick and Kevin Wayne.
*
* This file is part of algs4.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.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.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.jar. If not, see http://www.gnu.org/licenses.
******************************************************************************/