AVL Trees in TikZ: draw outside of node

Question

I'm trying to draw an AVL tree with TikZ. I got the basic tree structure covered, but I'm not sure how to draw the balance factor outside of the node (see picture below).

Any suggestions?

Answer 1

One option is to add labels to the nodes in the tree, e.g.

\documentclass{standalone}
\usepackage{tikz}
\begin{document}

\begin{tikzpicture}[
   edge from parent path=
    {(\tikzparentnode.south) .. controls +(0,-.5) and +(0,.5)
                             .. (\tikzchildnode.north)},
   every node/.style={draw,circle},
   label distance=-1mm]
\node [label=330:$-1$]{50}
  child {node[label=330:$-1$] {10}}
  child {node[label=330:$0$] {20}
  child {node[label=330:$-1$] {10}}
  child {node[label=330:$-1$] {20}}
};
\end{tikzpicture}
\end{document}