如何使箭头垂直居中？

Question

\documentclass{article}
\usepackage{amssymb}
\usepackage{tikz}
\begin{document}

\begin{itemize}
    \item \textbf{HEAPIFY(A, 7)}\\
          \begin{tikzpicture}
            \node{4}
            child { node {21} }
            child { node {14} };
          \end{tikzpicture}
          $\rightsquigarrow$
          \begin{tikzpicture}
            \node{21}
            child { node {4} }
            child { node {14} };
          \end{tikzpicture}

\end{itemize}
\end{document}

上述代码产生以下输出：

我想根据图表的总高度（而不是 14 和 4 的高度）将箭头垂直居中。该怎么做？

Answer 1

有几种选择，也许最简单的是

1. 适当地设置sbaseline的tikzpicture，或者
2. 用于remember picture添加overlay包含箭头的路径。

前两个示例将图的基线设置为底部节点，另两个示例将其基线设置为中心。

\documentclass{article}
\usepackage{amssymb}
\usepackage{tikz}
\begin{document}

\begin{itemize}
    \item \textbf{HEAPIFY(A, 7)}\\
          \begin{tikzpicture}[baseline={(14.base)}]
            \node{4}
            child { node {21} }
            child { node (14){14} };
          \end{tikzpicture}
          $\rightsquigarrow$
          \begin{tikzpicture}[baseline={(14.base)}]
            \node{21}
            child { node {4} }
            child { node (14){14} };
          \end{tikzpicture}
    \item \textbf{HEAPIFY(A, 7)}\\
          \begin{tikzpicture}[remember picture]
            \node{4}
            child { node {21} }
            child { node (14){14} };
          \end{tikzpicture}
          $\hphantom{\rightsquigarrow}$
          \begin{tikzpicture}[remember picture]
            \node{21}
            child { node (4) {4} }
            child { node {14} };
            \path[overlay] (14) -- node{$\rightsquigarrow$}(4);
          \end{tikzpicture}

    \item \textbf{HEAPIFY(A, 7)}\\
          \begin{tikzpicture}[baseline={(aux.base)}]
            \node (4) {4}
            child { node {21} }
            child { node (14){14} };
            \path (4) -- node(aux){\vphantom{x}}(14) ;
          \end{tikzpicture}
          $\rightsquigarrow$
          \begin{tikzpicture}[baseline={(aux.base)}]
            \node(21){21}
            child { node {4} }
            child { node (14){14} };
            \path (21) -- node(aux){\vphantom{x}} (14) ;
          \end{tikzpicture}
    \item \textbf{HEAPIFY(A, 7)}\\
          \begin{tikzpicture}[remember picture]
            \node(4){4}
            child { node {21} }
            child { node (14){14} };
          \end{tikzpicture}
          $\hphantom{\rightsquigarrow}$
          \begin{tikzpicture}[remember picture]
            \node(21){21}
            child { node (4') {4} }
            child { node {14} };
            \path[overlay] (4) --  node(aux1){\vphantom{x}}(14)
            (21) --  node(aux2){\vphantom{x}} (4')
             (aux1) -- node{$\rightsquigarrow$}(aux2);
          \end{tikzpicture}

\end{itemize}
\end{document}