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LoopQueue.java
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95 lines (80 loc) · 2.12 KB
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public class LoopQueue<E> implements Queue<E> {
private E[] data;
private int front, tail;
private int size;
public LoopQueue(int capacity) {
data = (E[]) new Object[capacity + 1];
front = 0;
tail = 0;
size = 0;
}
public LoopQueue() {
this(10);
}
public int getCapacity() {
return data.length - 1;
}
@Override
public boolean isEmpty() {
return front == tail;
}
@Override
public int getSize() {
return size;
}
@Override
public void enqueue(E e) {
if((tail + 1) % data.length == front) {
resize(getCapacity() * 2);
}
data[tail] = e;
tail = (tail + 1) % data.length;
size ++;
}
@Override
public E dequeue() {
if(isEmpty()) {
throw new IllegalArgumentException("Cannot dequeue from an empty queue.");
}
E ret = data[front];
data[front] = null;
front = (front + 1) % data.length;
size --;
if(size == getCapacity() / 4 && getCapacity() / 2 != 0) {
resize(getCapacity() / 2);
}
return ret;
}
@Override
public E getFront()
{
if(isEmpty()){
throw new IllegalArgumentException("Queue is empty.");
}
return data[front];
}
private void resize(int newCapacity)
{
// Create new capacity
E[] newData = (E[]) new Object[newCapacity + 1];
for (int i = 0; i < size; i ++) {
newData[i] = data[(i + front) % data.length];
}
data = newData;
front = 0;
tail = size;
}
public String toString() {
StringBuffer res = new StringBuffer();
res.append(String.format("Queue: size = %d, capacity = %d\n", size, getCapacity()));
res.append("front [");
for(int i = front; i != tail; i = (i + 1) % data.length) {
res.append(data[i]);
if((i + 1) % data.length != tail) {
res.append(", ");
}
}
res.append("] tail");
return res.toString();
}
}