/// <summary>
/// 雙向連結串列節點
/// </summary>
/// <typeparam name="T"></typeparam>
public class BdNode<T>
{
	public T Data { set; get; }
	public BdNode<T> Next { set; get; }
	public BdNode<T> Prev { set; get; }
	public BdNode(T val, BdNode<T> prev, BdNode<T> next)
	{
		this.Data = val;
		this.Prev = prev;
		this.Next = next;
	}
}
 

public class DoubleLink<T>
{
	//表頭
	private readonly BdNode<T> _linkHead;
	//節點個數
	private int _size;
	public DoubleLink()
	{
		_linkHead = new BdNode<T>(default(T), null, null);//雙向連結串列 表頭為空
		_linkHead.Prev = _linkHead;
		_linkHead.Next = _linkHead;
		_size = 0;
	}
	public int GetSize() => _size;
	public bool IsEmpty() => (_size == 0);
	//通過索引查詢
	private BdNode<T> GetNode(int index)
	{
		if (index < 0 || index >= _size)
			throw new IndexOutOfRangeException("索引溢位或者連結串列為空");
		if (index < _size / 2)//正向查詢
		{
			BdNode<T> node = _linkHead.Next;
			for (int i = 0; i < index; i++)
				node = node.Next;
			return node;
		}
		//反向查詢
		BdNode<T> rnode = _linkHead.Prev;
		int rindex = _size - index - 1;
		for (int i = 0; i < rindex; i++)
			rnode = rnode.Prev;
		return rnode;
	}
	public T Get(int index) => GetNode(index).Data;
	public T GetFirst() => GetNode(0).Data;
	public T GetLast() => GetNode(_size - 1).Data;
	// 將節點插入到第index位置之前
	public void Insert(int index, T t)
	{
		if (_size < 1 || index >= _size)
			throw new Exception("沒有可插入的點或者索引溢位了");
		if (index == 0)
			Append(_size, t);
		else
		{
			BdNode<T> inode = GetNode(index);
			BdNode<T> tnode = new BdNode<T>(t, inode.Prev, inode);
			inode.Prev.Next = tnode;
			inode.Prev = tnode;
			_size++;
		}
	}
	//追加到index位置之後
	public void Append(int index, T t)
	{
		BdNode<T> inode;
		if (index == 0)
			inode = _linkHead;
		else
		{
			index = index - 1;
			if (index < 0)
				throw new IndexOutOfRangeException("位置不存在");
			inode = GetNode(index);
		}
		BdNode<T> tnode = new BdNode<T>(t, inode, inode.Next);
		inode.Next.Prev = tnode;
		inode.Next = tnode;
		_size++;
	}
	public void Del(int index)
	{
		BdNode<T> inode = GetNode(index);
		inode.Prev.Next = inode.Next;
		inode.Next.Prev = inode.Prev;
		_size--;
	}
	public void DelFirst() => Del(0);
	public void DelLast() => Del(_size - 1);
	public void ShowAll()
	{
		Console.WriteLine("******************* 連結串列資料如下 *******************");
		for (int i = 0; i < _size; i++)
			Console.WriteLine("(" + i + ")=" + Get(i));
		Console.WriteLine("******************* 連結串列資料展示完畢 *******************\n");
	}
}