[Tex/LaTex] Draw a binary tree using tikz

tikz-pgftikz-treestrees

I'm trying to draw a binary tree using tikz package.

If I use only circle, I get a tree. But I want to represent a subtree using a triangle. Now the tree gets uneven. I want to attach the arrows to the top of the triangle and also want the size of the triangle comparable to the size of the circle.

\documentclass{article}
\usepackage{tikz}
\usepackage{pgfplots}
\pgfplotsset{compat=1.10}
\usetikzlibrary{shapes.geometric,arrows,fit,matrix,positioning}
\tikzset
{
    treenode/.style = {circle, draw=black, align=center, minimum size=1cm},
    subtree/.style  = {isosceles triangle, draw=black, align=center, minimum height=0.5cm, minimum width=1cm, shape border rotate=90, anchor=north}
}
\begin{document}
\begin{figure}[t]
\centering

\caption{An illustration of a simple delete operation. \label{fig:simple}}
{
    \begin{tikzpicture}[->,>=stealth',level/.style={sibling distance = 5cm/#1,
    level distance = 1.5cm},scale=0.6, transform shape]
    \node [treenode] {$X$ \\ 100}
    child
    {
        node [treenode] {$Y$ \\ 50} 
        child
        {
            node [treenode] {$Z$ \\ 40} 
            child
            {
                node [treenode] {$S1$ \\ 30} 
            }
            child
            {
                node [treenode] {$S2$ \\ 60} 
            }
        }
        child
        {
            node [subtree] {$Z$ \\ 200} 
        }
    }
    child
    {
        node [subtree] {$Z$ \\ 200} 
    }
;
    \end{tikzpicture}
}
\end{figure}
\end{document}

output

Best Answer

  1. With the OP's current setting the circles and triangles are of comparable size as long as the text is not written into the subtree nodes. So a possible solution is to write the text later after the drawing is done. This is shown by the last 2 lines of codes.

  2. To have the arrows pointing to the tip of a triangle, the following line is added to the corresponding parent nodes

    edge from parent path ={(\tikzparentnode.-50) -- (\tikzchildnode.north)} % -50 is adjustable.

  3. If the triangles are still incomparable, one can write scale=0.9 into the subtree style for shrinking adjustment.

enter image description here

Code

\documentclass{article}
\usepackage[paper size={10cm,8cm}]{geometry}
\usepackage{tikz}
\usepackage{pgfplots}
\pgfplotsset{compat=newest}
\usetikzlibrary{shapes.geometric,arrows,fit,matrix,positioning}
\tikzset
{
    treenode/.style = {circle, draw=black, align=center, minimum size=1cm},
    subtree/.style  = {isosceles triangle, draw=black, align=center, minimum height=0.5cm, minimum width=1cm, shape border rotate=90, anchor=north}
}
\begin{document}
\begin{figure}[t]
\centering

\caption{An illustration of a simple delete operation. \label{fig:simple}}
{
    \begin{tikzpicture}[->,>=stealth', level/.style={sibling distance = 5cm/#1, level distance = 1.5cm}, scale=0.6,transform shape]
    \node [treenode] {$X$ \\ 100}
    child
    {
        node [treenode] {$Y$ \\ 50} 
        child
        {
            node [treenode] {$Z$ \\ 40} 
            child
            {
                node [treenode] {$S1$ \\ 30} 
            }
            child
            {
                node [treenode] {$S2$ \\ 60} 
            }
        }
        child[edge from parent path ={(\tikzparentnode.-50) -- (\tikzchildnode.north)}]
        {
            node [subtree,yshift=0.4cm] (a) {}   % delay the text till later
        }
    }
    child[edge from parent path ={(\tikzparentnode.-30) -- (\tikzchildnode.north)}]
    {
        node [subtree,yshift=0.4cm] (b) {}       % delay the text till later
    }
;
% ------------------------------------------------ put the text into subtree nodes
\node[align=center,yshift=0.1cm] at (a) {$Z$\\200};
\node[align=center,yshift=0.1cm] at (b) {$Z$\\200};
\end{tikzpicture}
}
\end{figure}
Related Question