\documentclass{article}
\usepackage[pdftex,active,tightpage]{preview}
\setlength\PreviewBorder{2mm}

\usepackage[utf8]{inputenc} % this is needed for umlauts
\usepackage[ngerman]{babel} % this is needed for umlauts
\usepackage[T1]{fontenc}    % this is needed for correct output of umlauts in pdf
\usepackage{amssymb,amsmath,amsfonts} % nice math rendering
\usepackage{braket} % needed for \Set
\usepackage{algorithm,algpseudocode}

\DeclareMathOperator*{\argmin}{arg\,min}

\begin{document}
\begin{preview}
    \begin{algorithm}[H]
        \begin{algorithmic}
        \Require Trainingsdaten $X$ jeweils mit Klasse $K(X)$, Attribute~$A$,
                 Qualitätsfunktion $\varphi$
        \Procedure{ID3}{$X$, $A$}
            \If{$K(x_i) = K(x_j) \;\;\;\forall x_i, x_j \in X$}
                \State \Return Klasse $K(x_0)$
            \Else
                \State $a_\text{min} \gets \argmin_{a \in A} \varphi(a)$
                \State $n \gets \Call{CreateNode}{}$
                \For{Attributwert $w$ in $a_\text{min}(X)$}
                    \State $X_{a_\text{min} = w} \gets \{x \in X | a_\text{min}(X) = w\}$
                    \State $child \gets \Call{ID3}{X_{a_\text{min}}, A}$
                    \State $n.\Call{AddChild}{child}$
                \EndFor
                \State \Return $n$
            \EndIf
        \EndProcedure
        \end{algorithmic}
    \caption{ID3 Algorithmus}
    \label{alg:ID3}
    \end{algorithm}
\end{preview}
\end{document}