ResizingArrayStack.java

/* *****************************************************************************
 *  Name:              Ada Lovelace
 *  Coursera User ID:  123456
 *  Last modified:     October 16, 1842
 **************************************************************************** */

import edu.princeton.cs.algs4.StdIn;
import edu.princeton.cs.algs4.StdOut;

import java.util.Iterator;

public class ResizingArrayStack<T> implements Iterable<T> {
    private T[] a = (T[]) new Object[1];
    private int N;

    public boolean isEmpty() {
        return N == 0;
    }

    public int size() {
        return N;
    }

    public T pop() {
        T item = a[--N];
        a[N] = null; // loitering
        if (N > 0 && N == a.length / 4)
            resize(a.length / 2);
        return item;
    }

    public void resize(int max) {

        T[] temp = (T[]) new Object[max];
        for (int i = 0; i < N; i++) {
            temp[i] = a[i];
        }
        a = temp;
    }

    public void push(T item) {
        if (N == a.length)
            resize(2 * a.length);
        a[N++] = item;
    }

    public Iterator<T> iterator() {
        return new ReverseArrayIterator();
    }

    private class ReverseArrayIterator implements Iterator<T> {
        private int i = N;

        public boolean hasNext() {
            return i > 0;
        }

        public T next() {
            return a[--i];
        }
    }

    public static void main(String[] args) {
        ResizingArrayStack<String> s;
        s = new ResizingArrayStack<String>();
        while (!StdIn.isEmpty()) {
            String item = StdIn.readString();
            if (!item.equals("-")) {
                s.push(item);
            }
            else if (!s.isEmpty()) {
                StdOut.println(s.pop() + " ");
            }
        }
        StdOut.println(s.size() + " left on stack");
    }
}