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package torea;
class Queue{
public static class ArrayQueue<Item> implements IQueue<Item>
{
private int head;
private int tail;
private int size;
private Item[] array;
ArrayQueue(){
initializeArray(16);
}
@SuppressWarnings("unchecked")
private void initializeArray(int max){
array = (Item[]) new Object[max];
head = 0;
tail = 0;
size = max;
}
@SuppressWarnings("unchecked")
private void resize(int max){
Item[] old_array = array;
array = (Item[]) new Object[max];
int elementsToMove = size - freeElements();
for(int i = 0; i< elementsToMove; i++){
int oldIndex = (tail+i)%size;
array[i] = old_array[oldIndex];
}
tail = 0;
head = elementsToMove;
size = max;
}
private int freeElements(){
if (head >= tail){
return size - (head-tail);
} else {
return tail - head;
}
}
@Override
public boolean empty() {
return head == tail;
}
@Override
public Item dequeue() {
if(empty()) return null;
Item out = array[tail];
array[tail] = null;
tail = (tail+1)%size;
if((size>16) && (4*freeElements() >= 3*size)){
resize(size/2);
}
return out;
}
@Override
public Item peek() {
return array[tail];
}
@Override
public void enqueue(Item item) {
array[head] = item;
head = (head+1)%size;
if(freeElements()==1){
resize(size*2);
}
}
}
public static class LinkedListQueue<Item> implements IQueue<Item>
{
private Node first = null;
private Node last = null;
private int n;
private class Node
{
Item item;
Node next;
}
@Override
public boolean empty() {
return first == null;
}
@Override
public Item dequeue() {
Item item = first.item;
first = first.next;
n--;
if(empty()) last = null;
return item;
}
@Override
public Item peek() {
return first.item;
}
@Override
public void enqueue(Item item) {
Node old_last = last;
last = new Node();
last.item = item;
last.next = null;
if(empty()) first = last;
else old_last.next = last;
n++;
}
}
} |