删除目录中的缩进

Question

我想删除目录中的\section、\subsection和的空间\subsubsection。

这是我的代码：

\documentclass{book}
\usepackage[utf8]{inputenc}
\usepackage{imakeidx}
\makeindex[columns=3, title=Alphabetical Index, intoc]

\begin{document}

\tableofcontents
\chapter{chapter}
\section{Introduction}
In this example several keywords\index{keywords} will be 
used which are important and deserve to appear in the 
Index\index{Index}.
 \subsection{subsection}
Terms like generate\index{generate} and some\index{others} 
will also show up. Terms in the index can also be 
nested \index{Index!nested}

\clearpage

\section{Second section}
This second section\index{section} may include some special 
word, and expand the ones already used\index{keywords!used}.

\printindex
\end{document}

Answer 1

使用tocloft，这些长度由包括（for ）、（for ）和（for ）的\cftXindent其中之一管理：Xchap\chaptersec\sectionsubsec\subsection

\documentclass{book}

\usepackage{lipsum}
\usepackage{tocloft}

\setlength{\cftsecindent}{0pt}% Remove indent for \section
\setlength{\cftsubsecindent}{0pt}% Remove indent for \subsection
% \setlength{\cftsubsubsecindent}{0pt}% Remove indent for \subsubsection

\begin{document}

\tableofcontents

\chapter{A chapter}
\section{First section}\lipsum[1-5]
\subsection{A subsection}\lipsum[6-10]
\section{Second section}\lipsum[11-15]

\end{document}

Answer 2

解决方案如下titletoc：

 \documentclass{book}
 \usepackage[showframe]{geometry}
\usepackage[utf8]{inputenc}
\usepackage{imakeidx}
\makeindex[columns=3, title=Alphabetical Index, intoc]
\usepackage{titletoc}
\contentsmargin{0.2pt}
\titlecontents{section}
  [2.5em]
  {\vspace*{\baselineskip}\mdseries}
  {\contentslabel[\thecontentslabel]{2.5em}}
  {}
{\hfill\thecontentspage}
\titlecontents{subsection}
  [2.5em]
  {\vspace*{\baselineskip}\mdseries}
  {\contentslabel[\thecontentslabel]{2.5em}}
  {}
{\hfill\thecontentspage}
  []

\begin{document}

\tableofcontents
\chapter{chapter}
\section{Introduction}
In this example several keywords\index{keywords} will be
used which are important and deserve to appear in the
Index\index{Index}.
 \subsection{subsection}
Terms like generate\index{generate} and some\index{others}
will also show up. Terms in the index can also be
nested \index{Index!nested}

\clearpage

\section{Second section}
This second section\index{section} may include some special
word, and expand the ones already used\index{keywords!used}.

\printindex

\end{document}