[Tex/LaTex] How to make a enumerate list with no indent and no left margin like this

Question

I thank so much if anybody makes a enumerate list like this:

Problem 1. Text text text text ……………….. text text text text text text text text text text text text text text text text.

Problem 2. Text text text text ……………….. text text text text text text text text texttext text text text text text text .

Problem 3.

a) Text text text text ……………….. text text text text text text text text text text text text text text text text.

b) Text text text text ……………….. text text text text text text text text texttext text text text text text text .

Here are the codes:

\documentclass[12pt,a4paper]{article}
\usepackage{blindtext}
\begin{document}
\noindent I want to make a enumerate list like this:\\
\textbf{Problem 1.} \blindtext. \\
\textbf{Problem 2.}  \blindtext. \\
\textbf{Problem 3.} \\
a) \blindtext.\\
b) \blindtext.\\
\end{document}

Answer 1

Here is a way with enumitem: I define a \problems (level 1+2) list environment and a questions environment, which is to be used semantically as problems, level 2(but technically, nothing prevents you to use it at the first level). Similarly, I defined two clones of \item, \pb and \qu.

\documentclass[12pt, a4paper]{article}
\usepackage[utf8]{inputenc}
\usepackage[T1]{fontenc}
\usepackage{lmodern}

\usepackage[showframe]{geometry}
\usepackage{blindtext}

\usepackage{enumitem}
\newlist{problems}{enumerate}{2}
\setlist[problems, 1]{label=Problem~\arabic*. , font=\bfseries,  wide=0pt}%
\setlist[problems, 2]{label=\emph{alph*}),  wide=0pt, before=\leavevmode, topsep=0pt}%
\newenvironment{questions}{\problems}{\endproblems}
\let\pb\item
\let\qu\item

\begin{document}

Text text text text text text text text text text text text text text text text text text text text text text text text text text text text.
\begin{problems}
  \pb \blindtext
  \pb \blindtext
  \item
  \begin{questions}
    \qu \blindtext
    \qu \blindtext
  \end{questions}
\end{problems}

\end{document}