20 怎样用 tikz“快速”画树

如果你不介意重复绘制的话，下面也许是可行的...

\documentclass[landscape]{article}
\usepackage[margin=1in,a3paper]{geometry}
\usepackage{tkz-graph}
\begin{document}
\ExplSyntaxOn
\cs_new_protected:Npn \draw_dot_diagram:n #1
{
    \pgfmathtruncatemacro{\NN}{0}
    \str_set:Nn \l_tmpa_str { #1 }
    \seq_clear:N \l_tmpa_seq
    \begin{tikzpicture}[
        line~join=round,line~cap=round,
        VertexStyle/.style = {
            shape=circle,draw,fill,
            minimum~size=5pt,
            inner~sep=0pt,
            outer~sep=0pt,
        }]
        \SetGraphUnit{2}
        \SetVertexNoLabel
        \Vertex{P\NN}
        \str_map_inline:Nn \l_tmpa_str
        {
            \pgfmathtruncatemacro{\tmp}{\NN+1}
            \str_case:nn { ##1 }
            {
                {U} {\NO(P\NN){P\tmp}}
                {D} {\SO(P\NN){P\tmp}}
                {L} {\WE(P\NN){P\tmp}}
                {R} {\EA(P\NN){P\tmp}}
            }
            \Edge(P\NN)(P\tmp)
            \pgfmathtruncatemacro{\NN}{\tmp}
        }
    \end{tikzpicture}
    \par \vspace*{3cm}
}
\draw_dot_diagram:n {RRUDRUDRR}

\draw_dot_diagram:n {RRRUDRUDRUDRR}

\draw_dot_diagram:n {RRRURUDLUUDLRDDDRRLDRURRUUDR}
\ExplSyntaxOff
\end{document}

其实重复绘制的问题应该是有优化空间的，但我下午还有课...