tikz-graph 树的最后一层仅被圈出

Question

我怎样才能只圈出树的最后一层（叶子）（而不是所有层）？

\documentclass[tikz,border=10pt]{standalone}

\usetikzlibrary{graphdrawing}
\usetikzlibrary{graphs}
\usegdlibrary{trees}
\begin{document}

\tikzset{ every node/.style={circle, draw, fill=gray!10,, minimum size=0.75cm} }

\begin{tikzpicture}[>=stealth]

\graph [tree layout, grow=down, fresh nodes, level distance=0.5in, sibling distance=0.5in]
    {
        200 -> { 
          5 -> { 2, 2.5 },
         40 -> { 5 -> {2, 2.5 }, 8->{2,4} } 
        } 
    };
\end{tikzpicture}
\end{document}

Answer 1

不要将样式应用于，而是创建仅适用于选定节点的every node新样式。circnode

或者，您可以考虑使用forest非常简单的地方。

\RequirePackage{luatex85}
\documentclass[tikz,border=10pt]{standalone}
\usepackage{forest}

\usetikzlibrary{graphdrawing}
\usetikzlibrary{graphs}
\usegdlibrary{trees}
\begin{document}

\tikzset{ circnode/.style={circle, draw, fill=gray!10,, minimum size=0.75cm} }

\begin{tikzpicture}[>=stealth]

\graph [tree layout, grow=down, fresh nodes, level distance=0.5in, sibling distance=0.5in]
    {
        200 -> { 
          5 -> { 2 [circnode], 2.5 [circnode]},
         40 -> { 5 -> {2[circnode], 2.5[circnode] }, 8->{2[circnode],4[circnode]} } 
        } 
    };
\end{tikzpicture}

\begin{forest}
for tree={l=0.5in,s sep=5mm,edge={-stealth}},
where n children=0{circnode}{}
[200
  [5
    [2][2.5]
  ]
  [40
    [5
      [2][2.5]
    ]
    [8
      [2][4]
    ]
  ]
]
\end{forest}
\end{document}

Answer 2

在阅读 Torbjorn, T. 之前，我也偶然发现了这个解决方案。

\tikzstyle{leaves}=[circle, draw, fill=gray!10, minimum size=0.75cm]

\begin{tikzpicture}[>=stealth]

\graph [tree layout, grow=down, fresh nodes, level distance=0.5in, sibling distance=0.5in]
{
    200 -> { 
      5 -> { 2[leaves], 2.5[leaves] },
     40 -> { 5 -> {2[leaves], 2.5[leaves] }, 8-> {2[leaves],4[leaves]} }
    } 
};
\end{tikzpicture}