Section and subsection TOC title formatting

Question

I'm putting together a template for college assignments. In order to systematize the writing, I've reformatted the section/subsection titles in the document so they read "Problem #number" and " Answer #number" respectively, without the need for manual entry.

My problem here is that the TOC doesn't put a title for each section and subsection, as there is no argument passed in the command. See this example:

\documentclass{article}
\usepackage{titlesec}
\titleformat{\section}{\large \bfseries}{Problem \arabic{section}}{2em}{}
\titleformat{\subsection}{\small \bfseries}{Answer \arabic{section}}{1em}{}
\begin{document}
\tableofcontents
\section{}
\subsection{}
\end{document}

Produces:

I understand that I can manually add a title for TOC doing:

\section[title]{}

And that I could define a new command that could do this for every section (and for every subsection), like this

\documentclass{article}
\usepackage{titlesec}
\titleformat{\section}{\large \bfseries}{Problem \arabic{section}}{2em}{}
\newcommand{\problem}[1]{\section[Problem \thesection]{#1}}
\begin{document}
\tableofcontents
\problem{}
\end{document}

That produces

But this shows the section number to the left of the title.

Is there a better way to make all titles in the TOC automatically display as in the document?

Answer 1

I was going to suggest using the exercise package, but discovered a bug in the TOC formatting (which I fixed).

One can reformat the header easily enough, if you don't like centering.

\documentclass{article}
\usepackage{exercise}
\ListOfExerciseInToc
\ExerciseLevelInToc{section}
\def\ExerciseName{Problem}
\def\AnswerName{Answer}
\makeatletter
\renewcommand{@@@ExeEnv}{%
    \pagebreak[1]\vskip\ExerciseSkipBefore
    @QuestionLevel1
    \refstepExecounter
    \begingroup@getExerciseInfo\ExerciseHeader
    \addcontentsline{\ext@exercise}{\toc@exercise}{\ExerciseName

        \theExercise\ \expandafter{\string\itshape \ExerciseTitle}\hspace{.66em}}% added \string
    \endgroup\AtBeginExercise}
\renewcommand{@@@ExeCmd}{%
    \ifnum@QuestionLevel=0
      \advance @QuestionLevel by 1
      \begin{list}{@getExerciseInfo\ExerciseListHeader}%
{\partopsep\Exepartopsep \labelsep\Exelabelsep \itemsep \Exesep%
\parsep\Exeparsep \topsep\Exetopsep \labelwidth\Exelabelwidth%
\leftmargin\Exeleftmargin \rightmargin\Exerightmargin}
    \else
      \termineliste{1}@EndExeBox
    \fi
    @selectExercise
    \global@Answerfalse@BeginExeBox\refstepExecounter%
    \addcontentsline{\ext@exercise}{\toc@exercise}{\ExerciseName

        \theExercise\ \expandafter{\string\itshape \expandafter\ExerciseTitle}\hspace{.66em}}% added \string
    \item\ignorespaces\AtBeginExercise
}
\makeatother
\begin{document}
\tableofcontents
\bigskip\hrule
\section{Normal section}
\begin{Exercise}
  Problem text here.
\end{Exercise}
\begin{Answer}
  Answer text here.
\end{Answer}
\end{document}

Answer 2

Requires a small modification of the entry of the TOC from \section to suppress the section number.

\documentclass{article}
\usepackage{titlesec}
\titleformat{\section}{\large \bfseries}{Problem \thesection}{2em}{}
\newcommand{\problem}[1]{%
    \section[Problem \thesection]{#1}
}
%% from https://tex.stackexchange.com/a/218675/161015
\makeatletter
\let\latexl@section\l@section
\def\l@section#1#2{\begingroup\let\numberline@gobble\latexl@section{#1}{#2}\endgroup}
\makeatother
\begin{document}
    \tableofcontents
\problem{One}

\problem{Two}

\problem{Three}


\end{document}