将树的方向改为水平

Question 1

像这样？

使用forest超出了我暂时的能力，但使用 pure 的解决方案tikz非常简单：

\documentclass[tikz,border=5pt]{standalone}
\usetikzlibrary{chains, positioning, quotes, shapes}
\makeatletter
\tikzset{
  off chain/.code={\def\tikz@lib@on@chain{}}%
}
\makeatother

\begin{document}
\begin{tikzpicture}[auto,
node distance = 11mm and 22mm,
  start chain = A going right,
N/.style = {% Node
            ellipse, draw, minimum size=5mm,
            inner sep=1mm, outer sep=0mm,
            on chain=A},
every chain label/.style={inner sep=1mm, font=\footnotesize}
                                 ]
\node [N] {1,2};
\node [N] {2,3};
\node [N] {3,6};
\node [N] {6,7};
%
\node (n1) [N, off chain, below=of A-2] {2,5};
\node (n2) [N, off chain, below=of A-3] {3,4};
%
\draw   (A-1) to ["${1,3|2}$"] (A-2)
        (A-2) to ["${2,6|3}$"] (A-3)
        (A-3) to ["${3,7|6}$"] (A-4)
%
        (A-2) to ["${3,5|2}$"] (n1)
        (A-2) to ["${2,4|3}$"] (n2);
\end{tikzpicture}
\end{document}

附录（1）： 如果您喜欢使用带有粗体字母的彩色节点，如下所示：

那么您唯一需要做的就是在节点样式的定义中添加两行：

N/.style = {% Node
            ellipse, draw, minimum size=5mm,
            top color=white, bottom color=blue!20, % <-- added color to nodes
            font=\bfseries,                        % <-- added boldface to node content
            inner sep=1mm, outer sep=0mm,
            on chain=A},

附录（2）： 如果你喜欢你定义的样式（在其他forest情况下使用），那么你只需要更改tikzpicture节点的选项和名称。在这种情况下，完整的姆韦是：

\documentclass[tikz,border=5pt]{standalone}
\usetikzlibrary{chains, positioning, quotes, shapes}
\makeatletter
\tikzset{
  off chain/.code={\def\tikz@lib@on@chain{}}%
}
\makeatother

\tikzset{
  treenode/.style = {align=center, inner sep=0pt,
                     text centered, font=\sffamily,
                     top color=white, bottom color=blue!20},
       arn/.style = {treenode, circle, font=\sffamily\bfseries,
                    draw=black, fill=white, text width=6.5ex},
        }

\begin{document}
\begin{tikzpicture}[auto,
node distance = 11mm and 22mm,
  start chain = A going right,
every chain label/.style={inner sep=1mm, font=\footnotesize},
arn/.append style = {on chain=A}
                                 ]
\node [arn] {1,2};
\node [arn] {2,3};
\node [arn] {3,6};
\node [arn] {6,7};
%
\node (n1) [arn, off chain, below=of A-2] {2,5};
\node (n2) [arn, off chain, below=of A-3] {3,4};
%
\draw   (A-1) to ["${1,3|2}$"] (A-2)
        (A-2) to ["${2,6|3}$"] (A-3)
        (A-3) to ["${3,7|6}$"] (A-4)
%
        (A-2) to ["${3,5|2}$"] (n1)
        (A-2) to ["${2,4|3}$"] (n2);
\end{tikzpicture}
\end{document}

Answer

像这样？

使用forest超出了我暂时的能力，但使用 pure 的解决方案tikz非常简单：

\documentclass[tikz,border=5pt]{standalone}
\usetikzlibrary{chains, positioning, quotes, shapes}
\makeatletter
\tikzset{
  off chain/.code={\def\tikz@lib@on@chain{}}%
}
\makeatother

\begin{document}
\begin{tikzpicture}[auto,
node distance = 11mm and 22mm,
  start chain = A going right,
N/.style = {% Node
            ellipse, draw, minimum size=5mm,
            inner sep=1mm, outer sep=0mm,
            on chain=A},
every chain label/.style={inner sep=1mm, font=\footnotesize}
                                 ]
\node [N] {1,2};
\node [N] {2,3};
\node [N] {3,6};
\node [N] {6,7};
%
\node (n1) [N, off chain, below=of A-2] {2,5};
\node (n2) [N, off chain, below=of A-3] {3,4};
%
\draw   (A-1) to ["${1,3|2}$"] (A-2)
        (A-2) to ["${2,6|3}$"] (A-3)
        (A-3) to ["${3,7|6}$"] (A-4)
%
        (A-2) to ["${3,5|2}$"] (n1)
        (A-2) to ["${2,4|3}$"] (n2);
\end{tikzpicture}
\end{document}

附录（1）： 如果您喜欢使用带有粗体字母的彩色节点，如下所示：

那么您唯一需要做的就是在节点样式的定义中添加两行：

N/.style = {% Node
            ellipse, draw, minimum size=5mm,
            top color=white, bottom color=blue!20, % <-- added color to nodes
            font=\bfseries,                        % <-- added boldface to node content
            inner sep=1mm, outer sep=0mm,
            on chain=A},

附录（2）： 如果你喜欢你定义的样式（在其他forest情况下使用），那么你只需要更改tikzpicture节点的选项和名称。在这种情况下，完整的姆韦是：

\documentclass[tikz,border=5pt]{standalone}
\usetikzlibrary{chains, positioning, quotes, shapes}
\makeatletter
\tikzset{
  off chain/.code={\def\tikz@lib@on@chain{}}%
}
\makeatother

\tikzset{
  treenode/.style = {align=center, inner sep=0pt,
                     text centered, font=\sffamily,
                     top color=white, bottom color=blue!20},
       arn/.style = {treenode, circle, font=\sffamily\bfseries,
                    draw=black, fill=white, text width=6.5ex},
        }

\begin{document}
\begin{tikzpicture}[auto,
node distance = 11mm and 22mm,
  start chain = A going right,
every chain label/.style={inner sep=1mm, font=\footnotesize},
arn/.append style = {on chain=A}
                                 ]
\node [arn] {1,2};
\node [arn] {2,3};
\node [arn] {3,6};
\node [arn] {6,7};
%
\node (n1) [arn, off chain, below=of A-2] {2,5};
\node (n2) [arn, off chain, below=of A-3] {3,4};
%
\draw   (A-1) to ["${1,3|2}$"] (A-2)
        (A-2) to ["${2,6|3}$"] (A-3)
        (A-3) to ["${3,7|6}$"] (A-4)
%
        (A-2) to ["${3,5|2}$"] (n1)
        (A-2) to ["${2,4|3}$"] (n2);
\end{tikzpicture}
\end{document}

Question 2

这是一个使用 Ti 的方法钾Z 的图形语法，但不依赖于需要 LuaTeX 的图形绘制算法。如果您乐于使用 LuaTeX，您可以做更多花哨（和更自动化）的事情。此外，真正理解这一点的人可能比我更自动地做到这一点，即使坚持使用 pdfTeX。（我无法弄清楚如何从放置规则中排除一个节点，所以最终手动放置它们。即便如此，语法也使代码非常简洁。）

\documentclass[border=11pt]{standalone}
\usepackage{tikz}
\usetikzlibrary{graphs,shapes.geometric,quotes}
\begin{document}
  \begin{tikzpicture}
  \graph [nodes={draw, ellipse}]%, grow right sep=10mm, branch down sep=10mm]
  { a/"1,2" --["$1, 3|2$"] b/"2,3"[x=1] -- {c/"3,6"[>"$2, 6|3$",x=2] --["$3, 7|6$"] f/"6,7"[x=3], d/"3,4"[>"$2, 4|3$", x=2, y=-1], e/"2,5"[>"$3, 5|2$", y=-1] } };
\end{tikzpicture}
\end{document}

如果你希望只改变图形的结构，并让其使用与森林树相同的样式，你可以应用 Ti钾Z 样式与图表类似。例如，

\documentclass[border=11pt]{standalone}
\usepackage{tikz}
\usetikzlibrary{graphs,shapes.geometric,quotes}
\begin{document}
\tikzset{% cwestiwn Wilmer Rojas: https://tex.stackexchange.com/q/387249/
  treenode/.style = {align=center, inner sep=0pt, text centered, font=\sffamily, top color=white, bottom color=blue!20},
  arn/.style = {treenode, circle, font=\sffamily\bfseries, draw=black, fill=white, text width=6.5ex},
}
\begin{tikzpicture}[x=15mm]
  \graph [nodes={arn}, edge quotes={midway, anchor=center, font=\footnotesize, fill=white}]%, grow right sep=10mm, branch down sep=10mm]
  { a/"1,2" --["$1, 3|2$"] b/"2,3"[x=1] -- {c/"3,6"[>"$2, 6|3$",x=2] --["$3, 7|6$"] f/"6,7"[x=3], d/"3,4"[>"$2, 4|3$", x=2, y=-1], e/"2,5"[>"$3, 5|2$", y=-1] } };
\end{tikzpicture}
\end{document}

在这种情况下，我会分离出边缘的样式，并在森林定义和图表中使用该样式。

\tikzset{%
  arn edges/.style={midway, #1, font=\footnotesize, text=black},
}%
\forestset{%
  my x/.style n args=2{
    edge label={node [arn edges={#2}] {$c_{#1}$}},
  },
}%
...
\graph [nodes={arn}, edge quotes={arn edges={fill=white}}] ...

等等。

由于这里没有加载 Forest 设置，因此我们将其忽略，这样我们

\documentclass[border=11pt]{standalone}
\usepackage{tikz}
\usetikzlibrary{graphs,shapes.geometric,quotes}
\begin{document}
\tikzset{% cwestiwn Wilmer Rojas: https://tex.stackexchange.com/q/387249/
  treenode/.style = {align=center, inner sep=0pt, text centered, font=\sffamily, top color=white, bottom color=blue!20},
  arn/.style = {treenode, circle, font=\sffamily\bfseries, draw=black, fill=white, text width=6.5ex},
  arn edges/.style={midway, #1, font=\footnotesize, text=black},
}%
\begin{tikzpicture}[x=15mm]
  \graph [nodes={arn}, edge quotes={arn edges={fill=white}}]%, grow right sep=10mm, branch down sep=10mm]
  { a/"1,2" --["$1, 3|2$"] b/"2,3"[x=1] -- {c/"3,6"[>"$2, 6|3$",x=2] --["$3, 7|6$"] f/"6,7"[x=3], d/"3,4"[>"$2, 4|3$", x=2, y=-1], e/"2,5"[>"$3, 5|2$", y=-1] } };
\end{tikzpicture}
\end{document}

生成上面的第二张图像。

Answer