import java.util.Arrays;

public class ArrayQueue {
    private int length = 5;
    private Object[] queue = new Object[length];
    private int head = 0;
    private int tail = 0;

    public void enqueue(Object x) {
        ensureCapacity(size() + 1);
        queue[tail] = x;
        tail = (tail + 1) % length;
    }

    private void ensureCapacity(int capacity) {
        if (capacity > length) {
            length *= 2;
            queue = Arrays.copyOf(queue, length);
        }
    }

    public Object element() {
        assert size() != 0;

        return queue[head];
    }


    public Object dequeue() {
        if (isEmpty()) {
            return null;
        }
        Object x = queue[head];
        head = (head + 1) % length;
        return x;
    }

    public int size() {
        if (head > tail) {
            return length - head + tail;
        } else {
            return tail - head;
        }
    }

    public boolean isEmpty() {
        return head == tail;
    }

    public void clear() {
        queue = new Object[5];
        head = 0;
        tail = 0;
    }
}