queue.go
func (queue *queue) Peek() interface{} {
	if queue.size == 0 {
		return nil
	}
	return queue.elements[queue.start%int64(queue.cap)]
}
func (queue *queue) Peek() interface{} {
	if queue.size == 0 {
		return nil
	}
	return queue.elements[queue.start%int64(queue.cap)]
}
// Peek returns the element at the front of the queue.