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public static string DrawTree<T>(this BinaryTreeBase<T> tree) where T : IComparable<T>
{
    return string.Join("
", RecursivelyDrawTree(tree.Root, out _, out _));
}
private static List<string> RecursivelyDrawTree<T>(BTNode<T> node, out int positionOutput, out int widthOutput)
    where T : IComparable<T>
{
    positionOutput = widthOutput = 0;
    if (node == null)
    {
        return new List<string>();
    }
    // 结点内容标签
    var label = node.Data.ToString();
    var leftLines = RecursivelyDrawTree(node.LeftChild, out int leftPos, out int leftWidth);
    var rightLines = RecursivelyDrawTree(node.RightChild, out int rightPos, out int rightWidth);
    // 计算填充
    int middle = Math.Max(Math.Max(2, label.Length), (rightPos + leftWidth - leftPos + 1));
    int pos_out = leftPos + middle / 2;
    int width_out = leftPos + middle + rightWidth - rightPos;
    while (leftLines.Count < rightLines.Count)
    {
        leftLines.Add(new string(' ', leftWidth));
    }
    while (rightLines.Count < leftLines.Count)
    {
        rightLines.Add(new string(' ', rightWidth));
    }
    if ((middle - label.Length % 2 == 1) && (label.Length < middle) && (node.Parent != null && node.IsLeftChild))
    {
        label += ".";
    }
    // 格式化结点标签
    label = label.PadCenter(middle, '.');
    var lbChars = label.ToCharArray();
    if (lbChars[0] == '.')
    {
        lbChars[0] = ' ';
    }
    if (lbChars[lbChars.Length - 1] == '.')
    {
        lbChars[lbChars.Length - 1] = ' ';
    }
    label = string.Join("", lbChars);
    // 构造列表
    string leftBranch = node.HasLeftChild ? "/" : " ";
    string rightBranch = node.HasRightChild ? "\" : " ";
    var rslt = new List<string>()
    {
        (new string(' ',leftPos))+label+(new string(' ',(rightWidth-rightPos))),
        (new string(' ',leftPos))+leftBranch+(new string(' ',(middle-2)))+rightBranch+(new string(' ',(rightWidth-rightPos))),
    };
    // 将右线和左线添加到最终列表中
    rslt.AddRange(leftLines.Zip(rightLines, (left, right) => left + (new string(' ', (width_out - leftWidth - rightWidth))) + right));

    widthOutput = width_out;
    positionOutput = pos_out;
    return rslt;
}

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