1.3.40 #

/// <summary>
/// 前移编码队列。
/// </summary>
/// <typeparam name="TItem">需要前移编码的元素类型。</typeparam>
internal class MoveToFront<TItem>
{
    private class Node<T>
    {
        public T Item;
        public Node<T> Next;
    }

    private Node<TItem> _first;
    private int _count;

    /// <summary>
    /// 检查编码组是否为空。
    /// </summary>
    /// <returns></returns>
    public bool IsEmpty()
    {
        return _first == null;
    }

    /// <summary>
    /// 建立一个前移编码组。
    /// </summary>
    public MoveToFront()
    {
        _first = null;
        _count = 0;
    }

    /// <summary>
    /// 找到相应元素的前驱结点。
    /// </summary>
    /// <param name="item">要寻找的元素。</param>
    /// <returns></returns>
    private Node<TItem> Find(TItem item)
    {
        if (IsEmpty())
        {
            return null;
        }

        var current = _first;
        while (current.Next != null)
        {
            if (current.Next.Item.Equals(item))
            {
                return current;
            }
            current = current.Next;
        }
        return null;
    }

    /// <summary>
    /// 前移编码插入。
    /// </summary>
    /// <param name="item">需要插入的元素。</param>
    public void Insert(TItem item)
    {
        var temp = Find(item);
        if (temp == null)
        {
            temp = new Node<TItem>
            {
                Item = item,
                Next = _first
            };

            _first = temp;
            _count++;
        }
        else if (_count != 1)
        {
            var target = temp.Next;
            temp.Next = temp.Next.Next;
            target.Next = _first;
            _first = target;
        }
    }

    /// <summary>
    /// 查看第一个元素。
    /// </summary>
    /// <returns></returns>
    public TItem Peek()
    {
        if (_first == null)
        {
            throw new InvalidOperationException();
        }

        return _first.Item;
    }

    public override string ToString()
    {
        var s = new StringBuilder();
        var current = _first;
        while (current != null)
        {
            s.Append(current.Item.ToString());
            s.Append(" ");
            current = current.Next;
        }

        return s.ToString();
    }
}