/*************************************************************************
* Compilation: javac ResizingArrayQueue.java
* Execution: java ResizingArrayQueue < input.txt
* Data files: http://algs4.cs.princeton.edu/13stacks/tobe.txt
*
* Queue implementation with a resizing array.
*
* % java ResizingArrayQueue < tobe.txt
* to be or not to be (2 left on queue)
*
*************************************************************************/
public class ResizingArrayQueue<Item> implements Iterable<Item> {
private Item[] q; // queue elements
private int N = 0; // number of elements on queue
private int first = 0; // index of first element of queue
private int last = 0; // index of next available slot
// cast needed since no generic array creation in Java
public ResizingArrayQueue() {
q = (Item[]) new Object[2];
}
public boolean isEmpty() { return N == 0; }
public int size() { return N; }
// resize the underlying array
private void resize(int max) {
assert max >= N;
Item[] temp = (Item[]) new Object[max];
for (int i = 0; i < N; i++) {
temp[i] = q[(first + i) % q.length];
}
q = temp;
first = 0;
last = N;
}
public void enqueue(Item item) {
// double size of array if necessary and recopy to front of array
if (N == q.length) resize(2*q.length); // double size of array if necessary
q[last++] = item; // add item
if (last == q.length) last = 0; // wrap-around
N++;
}
// remove the least recently added item
public Item dequeue() {
if (isEmpty()) throw new NoSuchElementException("Queue underflow");
Item item = q[first];
q[first] = null; // to avoid loitering
N--;
first++;
if (first == q.length) first = 0; // wrap-around
// shrink size of array if necessary
if (N > 0 && N == q.length/4) resize(q.length/2);
return item;
}
public Iterator<Item> iterator() { return new ArrayIterator(); }
// an iterator, doesn't implement remove() since it's optional
private class ArrayIterator implements Iterator<Item> {
private int i = 0;
public boolean hasNext() { return i < N; }
public void remove() { throw new UnsupportedOperationException(); }
public Item next() {
if (!hasNext()) throw new NoSuchElementException();
Item item = q[(i + first) % q.length];
i++;
return item;
}
}
/**
* A test client.
*/
public static void main(String[] args) {
ResizingArrayQueue<String> q = new ResizingArrayQueue<String>();
while (!StdIn.isEmpty()) {
String item = StdIn.readString();
if (!item.equals("-")) q.enqueue(item);
else if (!q.isEmpty()) StdOut.print(q.dequeue() + " ");
}
StdOut.println("(" + q.size() + " left on queue)");
}
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