核心思想：利用求餘，讓索引迴圈

    class CircularQueue<T>
    {
        private T[] _queue;
        private int _head;
        private int _tail;
        private int _count;
        private int _capacity;

        public int Count
        {
            get
            {
                return _count;
                //return (_head - _tail + _capacity) % _capacity;不用計數器得到長度的方法
 

            }
        }

        public int Capacity
        {
            get { return _capacity; }
        }

        public CircularQueue(int capacity)
        {
            _capacity = capacity;
            _queue = new T[_capacity];
            _head = 0;
            _tail = 0;
            _count = 0
 
;
        }

        public bool IsFull()
        {
            return _count == _capacity;
            //return _head == (_tail + 1)%_capacity;不用計數器實現判滿的方法，需要犧牲一個空間
        }

        public bool IsEmpty()
        {
            return _count == 0;
            //return _head == _tail;不用計數器實現判空的方法
        }

        public
 
 void Enquene(T item)
        {
            if (IsFull())
            {
                Console.WriteLine("Queue is Full!");
                return;
            }
            _queue[_tail] = item;
            _tail = (_tail + 1) % _capacity;
            _count++;
        }

        public T Dequeue()
        {
            if (IsEmpty())
            {
                Console.WriteLine("Queue is Full!");
                return default(T);
            }
            T temp = _queue[_head];
            _head = (_head + 1) % _capacity;
            _count--;
            return temp;
        }

        public T Peek()
        {
            if (IsEmpty())
            {
                Console.WriteLine("Queue is Full!");
                return default(T);
            }
            return _queue[_head];
        }

        public void Clear()
        {
            Array.Clear(_queue, 0, _capacity);
            _head = 0;
            _tail = 0;
            _count = 0;
        }

        public bool Contains(T item)
        {
            int index = _head;
            for (int i = 0; i < _count; i++)
            {
                if (item.Equals(_queue[index]))
                {
                    return true;
                }
                index = (index + 1) % _capacity;
            }
            return false;
        }

        public void DisPlay()
        {
            int index = _head;
            for (int i = 0; i < _count; i++)
            {
                Console.WriteLine(_queue[index]);
                index = (index + 1) % _capacity;

            }

        }
    }