QueuePictures.tex

\documentclass{standalone}

\usepackage{tikz}
\usetikzlibrary{calc}

\def\cells#1#2#3{%
% #1 = total number of cells
% #2 = number of grey cells
% #3 = index for "front" ("back" is mod(#3+#2-1, #1))
  \foreach [count=\i from 0] \j  in {1,...,#1} {
    % \node[cell,label=above:\i] (cell\i) at (\i,0) {};
    \node[cell] (cell\i) at (\i,0) {};
  }
  \pgfmathsetmacro{\last}{#3+#2-1}
  \foreach \i in {#3,...,\last} {
    \pgfmathsetmacro{\back}{mod(\i,#1)}
    \node[shaded cell] (back) at (\back,0) {};
  }
  \node[below] at (cell#3.south) {front};
  \node[below] at (back.south) {back};
}

\tikzset{
  cell/.style = {draw, minimum width=1cm, minimum height=0.8cm},
  shaded cell/.style = {cell, fill=black!30},
}

\begin{document}
%\begin{tikzpicture}
%\cells{6}{3}{0}
%\end{tikzpicture} \\
%
%\begin{tikzpicture}
%\cells{6}{3}{3}
%\end{tikzpicture} \\
%
%\begin{tikzpicture}
%\cells{6}{3}{4}
%\end{tikzpicture} \\

\begin{tikzpicture}
\cells{8}{7}{0}
\foreach [count=\i from 0] \number in {$P_1[0]$, $P_2[0]$, $P_3[0]$, 299, 8, 14, 53, 78}
\node at (cell\i) {\number};
\end{tikzpicture}

\end{document}