TikZ-PGF：通过引用节点坐标在二叉树图内绘制曲线

Question

我一直在尝试在 TikZ 布局中表示旋转。在命名或为节点添加别名方面，我已经用尽了大多数选项，但没有任何运气。实际上，我试图理想地引用三个节点 {A、B、C} 的坐标，然后在这三个节点之间绘制一条从 A 开始到 C 的半圆形路径。下面是我的树块和相关包：

\documentclass{standalone}
\usepackage{tikz}
\usetikzlibrary{graphs,graphdrawing,arrows.meta}
\usegdlibrary{trees}
\tikzset{rn/.style      =   {draw=red, circle, dashed, inner sep=2pt, minimum size = 15pt, align=center}}
\tikzset{bn/.style      =   {draw, circle, double, inner sep=2pt, minimum size = 15pt, align=center}}
\tikzset{ebn/.style     =   {draw, circle, double, inner sep=1pt, minimum size = 5pt, align=center}}

\begin{document}

\begin{tikzpicture} [binary tree layout, scale=1.25]
    \node [bn] {30}
        child{node [bn] {20}
                child{node [ebn] {}}
                child{node [ebn] {}}
            }
        child{node [rn] {40}
            child{node [bn] {38}
                child{node (a) [rn] {35}
                    child{node [thick, rn] {31}}
                    child{node [ebn] {}}}
                child{node (b) [ebn] {}}
            }
            child{node [rn] {45}
                child{node [ebn] {}}
                child{node [ebn] {}}}
    };
    \draw [->] (a.east) arc (b.west);
\end{tikzpicture}

\end{document}

Answer 1

您非常接近，但是，arc这不是正确的命令。您想在三角形 {a,b,c} 内绘制一条曲线路径，您应该使用该controls操作。您还加载了各种库，但这些库都不是绘图所必需的。

\documentclass{standalone}
\usepackage{tikz}
\tikzset{
    rn/.style  = {draw=red, circle, dashed, inner sep=2pt, minimum size = 15pt, align=center},
    bn/.style  = {draw, circle, double, inner sep=2pt, minimum size = 15pt, align=center},
    ebn/.style = {draw, circle, double, inner sep=1pt, minimum size = 5pt, align=center},
}

\begin{document}

\begin{tikzpicture}[
        scale=1.25,
        level/.style={
            sibling distance=3cm/#1,
            level distance=1cm,
        },
    ]
    \node [bn] {30}
        child{node [bn] {20}
                child{node [ebn] {}}
                child{node [ebn] {}}
            }
        child{node [rn] {40}
            child{node (c) [bn] {38}
                child{node (a) [rn] {35}
                    child{node [thick, rn] {31}}
                    child{node [ebn] {}}}
                child{node (b) [ebn] {}}
            }
            child{node [rn] {45}
                child{node [ebn] {}}
                child{node [ebn] {}}}
    };
    \draw [ultra thick,red,shorten <=2pt,shorten >=2pt]
        (a) .. controls ([yshift=-.2cm]c) .. (b);
\end{tikzpicture}

\end{document}