在C#中实现双向枚举器

public class BiDirectionalEnumerator<T> : IEnumerator<T>
{
    private readonly List<T> _items;
    private int _currentIndex;
    private readonly int _startIndex;

    public BiDirectionalEnumerator(List<T> items, int startIndex)
    {
        _items = items;
        _currentIndex = startIndex;
        _startIndex = startIndex;
    }

    public bool MoveNext()
    {
        if (_currentIndex < _items.Count - 1)
        {
            _currentIndex++;
            return true;
        }
        return false;
    }

    public bool MovePrevious()
    {
        if (_currentIndex > 0)
        {
            _currentIndex--;
            return true;
        }
        return false;
    }

    public void Reset()
    {
        _currentIndex = _startIndex;
    }

    public T Current
    {
        get { return _items[_currentIndex]; }
    }

    object IEnumerator.Current
    {
        get { return Current; }
    }

    public void Dispose()
    {
    }
}

var items = new List<int> { 1, 2, 3, 4, 5 };
var enumerator = new BiDirectionalEnumerator<int>(items, 0);

while (enumerator.MoveNext())
{
    Console.WriteLine(enumerator.Current);
}

while (enumerator.MovePrevious())
{
    Console.WriteLine(enumerator.Current);
}