\hspace bagunça overbrace

Question

Gostaria de corrigir o overbrace incorreto e também colocar "ADD" sobre o array, mas sem divisor vertical, talvez um pouco mais com uma pequena linha apontando o primeiro elemento do array. Me desculpe, sou um novato e estou usando látex para um relatório universitário pela primeira vez. Este é o meu código:

\setbox0=\hbox{$
    \arrayrulecolor{black} % Color for table borders
    \rowcolors{1}{white}{gray!30} % Alternate gray backgrounds in rows
    \hspace{-2em}\begin{array}{|c|*{27}{c|}}
    ADD   \\
    \hline
    \textbf{128} & \hphantom{0}0 &
    \textbf{64} & \hphantom{0}0 &
    \textcolor{blue}{\textbf{\hphantom{0}0}}  & \hphantom{0}0 &
    \textcolor{blue}{\textbf{\hphantom{0}0}}& \hphantom{0}0 &
    \textcolor{blue}{\textbf{\hphantom{0}0}} & \hphantom{0}0 &
    \textcolor{blue}{\textbf{\hphantom{0}0}} & \hphantom{0}0 &
    \textcolor{blue}{\textbf{\hphantom{0}0}} & \hphantom{0}0 &
    \textbf{100} & \hphantom{0}0 &
    \textbf{1} & \hphantom{0}0 &
    \textcolor{blue}{\textbf{0}} & \hphantom{0}0  &
    \textbf{5} &  \hphantom{0}0 \\
    \hline
    \end{array}
$}

% Underbrace without left bracket
\[
  \overbrace{\usebox0}^{K}
\]



\begin{center}
    % Draw a down-facing arrow from "ADD" to the first element
    \begin{tikzpicture}
    % Downward arrow pointing from "ADD" to the first element
    \draw[->, thick] (0, 1.5) -- (0, 0.5); % Draw the down arrow
    \end{tikzpicture}
    \end{center}

    \vspace{-2.5em} % Negative space to bring elements closer
    
    \begin{center}
\[ 
    \arrayrulecolor{black} % Color for table borders
    \rowcolors{1}{gray!30}{gray!30} % Alternate gray backgrounds in rows
    \hspace{-2em}\begin{array}{|c|*{27}{c|}}
        \hline
    \hphantom{0}\textbf{128}\hphantom{0} & \textcolor{red}{31} &
    \textbf{64}& \textcolor{red}{31}&
    \textcolor{blue}{\textbf{64}}& \textcolor{red}{30}& 
    \textcolor{blue}{\textbf{64}}& \textcolor{red}{29}&
    \textcolor{blue}{\textbf{64}}& \textcolor{red}{28}& 
    \textcolor{blue}{\textbf{64}}& \textcolor{red}{27}& 
    \textcolor{blue}{\textbf{64}}& \textcolor{red}{26}& 
    \textbf{100}& \textcolor{red}{31}& 
    \textbf{1}& \textcolor{red}{31}& 
    \textcolor{blue}{\textbf{1}}& \textcolor{red}{30}& 
    \textbf{5}& \textcolor{red}{31} \\
    \hline
    
    \end{array} 
\]
\end{center}```

Answer 1

Não está muito claro o que você deseja, mas pode ser algo como o que segue.

1. Apenas um tabularambiente
2. Colunas têm largura fixa
3. O contraventamento só se estende sobre os pilares após “ADD”; como os pilares possuem largura fixa, é possível saber qual deve ser o comprimento do contraventamento.
4. Ajustei \tabcolseppara que a tabela possa ficar contida nas margens conforme definido por geometry; dependendo da sua configuração, você pode brincar com essa duração.

\documentclass{article}
\usepackage[a4paper]{geometry}
\usepackage[table]{xcolor}
\usepackage{array}
\usepackage{amsmath}

\newlength{\lenA}
\newlength{\lenB}

\begin{document}

\begin{center}
\small
\settowidth{\lenA}{ADD}
\settowidth{\lenB}{\textbf{00}}
\setlength{\tabcolsep}{3.7pt}

  \begin{tabular}{|w{c}{\lenA}|*{21}{w{c}{\lenB}|}}
    \multicolumn{1}{c}{\textrm{ADD}} &
    \multicolumn{1}{l}{\makebox[0pt][l]{%
      $\overbrace{\hspace{\dimeval{21\lenB+40\tabcolsep+20\arrayrulewidth}}}^K$%
    }}
   \\
    \hline
    \rowcolor{gray!30}% Alternate gray backgrounds in rows
    \textbf{128} & \hphantom{0}0 &
    \textbf{64} & \hphantom{0}0 &
    \textcolor{blue}{\textbf{\hphantom{0}0}} & \hphantom{0}0 &
    \textcolor{blue}{\textbf{\hphantom{0}0}} & \hphantom{0}0 &
    \textcolor{blue}{\textbf{\hphantom{0}0}} & \hphantom{0}0 &
    \textcolor{blue}{\textbf{\hphantom{0}0}} & \hphantom{0}0 &
    \textcolor{blue}{\textbf{\hphantom{0}0}} & \hphantom{0}0 &
    \textbf{100} & \hphantom{0}0 &
    \textbf{1} & \hphantom{0}0 &
    \textcolor{blue}{\textbf{0}} & \hphantom{0}0  &
    \textbf{5} &  \hphantom{0}0 \\
    \hline
    \multicolumn{1}{c}{} \\[-1.5ex]
    \multicolumn{1}{c}{$\left\downarrow\vbox to 15pt{}\right.$} \\
    \multicolumn{1}{c}{} \\[-1.5ex]
    \hline
    \rowcolor{gray!30} % Alternate gray backgrounds in rows
    \textbf{128} & \textcolor{red}{31} &
    \textbf{64}& \textcolor{red}{31}&
    \textcolor{blue}{\textbf{64}}& \textcolor{red}{30}& 
    \textcolor{blue}{\textbf{64}}& \textcolor{red}{29}&
    \textcolor{blue}{\textbf{64}}& \textcolor{red}{28}& 
    \textcolor{blue}{\textbf{64}}& \textcolor{red}{27}& 
    \textcolor{blue}{\textbf{64}}& \textcolor{red}{26}& 
    \textbf{100}& \textcolor{red}{31}& 
    \textbf{1}& \textcolor{red}{31}& 
    \textcolor{blue}{\textbf{1}}& \textcolor{red}{30}& 
    \textbf{5}& \textcolor{red}{31} \\
    \hline
  \end{tabular}
\end{center}

\end{document}