package queues;

public class QueueUsingArrays {

private int[] data;

private int front; // index of the element @ the front end of the queue

private int rear; // index of the element @ the last end of the queue

private int size;

public QueueUsingArrays() {

data = new int[5];

front = -1;

rear = -1;

}

public QueueUsingArrays(int capacity) {

data = new int[capacity];

front = -1;

rear = -1;

}

public int size() {

return size;

}

public boolean isEmpty() {

return size == 0;

}

public void enqueue(int element) {

if (size == data.length) {

doubleCapacity();

}

if (size == 0) {

front++;

}

rear = (rear + 1) % data.length;

data[rear] = element;

size++;

}

private void doubleCapacity() {

int[] tmp = data;

data = new int[tmp.length * 2];

int index = 0;

for (int i = front; i < tmp.length; i++) {

data[index++] = tmp[i];

}

for (int i = 0; i < front - 1; i++) {

data[index++] = tmp[i];

}

front = 0;

rear = tmp.length - 1;

}

public int front() {

if (size == 0) {

throw new IllegalArgumentException("Queue is Empty");

}

return data[front];

}

public int dequeue() {

if (size == 0) {

throw new IllegalArgumentException("Queue is Empty");

}

int tmp = data[front];

front = (front + 1) % data.length;

size--;

if (size == 0) {

front = -1;

rear = -1;

}

return tmp;

}

}