Coloring the lines of an algorithm

Question

I'm writing a report for a class project and I need to highlight several lines within some of the algorithms in the report. I managed to do so, but I don't like the solution I got. Here is a picture (see code of MWE below).

To get this, I used \color{red}, then put the text I wanted to highlight, followed by \color{black}. I wonder if I can highlight in red the same lines of the algorithm but not the line numbers and also not the comment a miracle in polynomial time. What solutions are there for this? This answer proposes redefining commands of the package but they are not using the same package as I am, and I wonder whether it can be made more simply or not.

If I could be given advice on how to do this, while sticking to the package algorithm2e, as far as it is possible, that would be great.

Code:

\documentclass[12pt]{article}
\pdfoutput=1
\usepackage[linesnumbered,titlenumbered,ruled,vlined,resetcount,algosection]{algorithm2e}
\usepackage[usenames,dvipsnames]{xcolor}
\usepackage{color}
\begin{document}
\title{MWE}
\maketitle
\section{Algorithm}
\begin{algorithm}
    \caption{3-SAT in polynomial time}
    \label{alg:hs}
    \DontPrintSemicolon
    \KwIn{List of clauses}
    \KwOut{The clauses are satisfiable}
    \SetKwProg{Fn}{Function}{ is}{end}
    \Fn{\textsc{IsSatisfiable}($C$)} {
    \color{red} %&lt;- my best attempt
    $k\gets 0$ \;
    \For {$i = 1$ \bf{to} $|C|$}
    {
        $c_i \gets $ $i$-th clause \;
        $L \gets$ list of literals of $c_i$ \;
        $k\gets f(k, L)$ \tcp{a miracle in polynomial time}
    }
    \color{black} %&lt;- go back to color black

    \If {$k$ is even} {
        \Return true
    }
    \Else {
        \Return false
    }

}

\end{algorithm}
\end{document}

score 5 · Accepted Answer · answered Jan 21 '21 at 16:02

I've never used algorithm2e but looking at its documentation (Sec. 9.5.3) I'd say the most sensible thing is to redefine the fonts for the numbers and comments to explicitly include a directive to switch the color to black.

\documentclass[12pt]{article}
\usepackage[linesnumbered,titlenumbered,ruled,vlined,resetcount,algosection]{algorithm2e}
\usepackage[usenames,dvipsnames]{xcolor}
\usepackage{color}
%% These three lines  !!!
\SetNlSty{textbf}{\color{black}}{}
\newcommand*{\mycommentfont}[1]{\textcolor{black}{\ttfamily#1}}
\SetCommentSty{mycommentfont}
\begin{document}
\title{MWE}
\maketitle
\section{Algorithm}
\begin{algorithm}
    \caption{3-SAT in polynomial time}
    \label{alg:hs}
    \DontPrintSemicolon
    \KwIn{List of clauses}
    \KwOut{The clauses are satisfiable}
    \SetKwProg{Fn}{Function}{ is}{end}
    \Fn{\textsc{IsSatisfiable}($C$)} {
        \begingroup
        \color{red}
        $k\gets 0$ ;
        \For {$i = 1$ \bf{to} $|C|$}
        {
            $c_i \gets $ $i$-th clause ;
            $L \gets$ list of literals of $c_i$ ;
            $k\gets f(k, L)$ \tcp{a miracle in polynomial time}
        }
        \endgroup

        \If {$k$ is even} {
            \Return true
        }
        \Else {
            \Return false
        }
}

\end{algorithm}
\end{document}

The extra definition of \mycommentfont is necessary because the font commands of algorithm2e expect a single macro name (without \) of a macro taking one argument.

Oh, wow! What a simple solution. I could've never come up with this, thank you! — Lluís Alemany-Puig, Jan 21 '21 at 16:54

Coloring the lines of an algorithm

1 Answers1