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regex questions added

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Joerg Kreiker 7 years ago
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  1. 35
      gsd-questions.tex

35
gsd-questions.tex

@ -93,9 +93,10 @@ Describe an algorithm to reverse a singly-linked list that \emph{does not}
copy any memory cells. copy any memory cells.
\ifdefined\loesung \ifdefined\loesung
\textcolor{red}{
{\bf Solution}: Maintain three pointers following each other: current, next, and {\bf Solution}: Maintain three pointers following each other: current, next, and
previous. The first pointer is one element ahead of the second. Reverse each pointer previous. The first pointer is one element ahead of the second. Reverse each pointer
as you you.
as you you.}
\fi \fi
\subsection{Preorder Tree Traversal} \subsection{Preorder Tree Traversal}
@ -109,21 +110,49 @@ Consider the following tree and state the \emph{preorder} and \emph{inorder} tra
\end{verbatim} \end{verbatim}
Which data structure do you need to implement such a traversal? Which data structure do you need to implement such a traversal?
\ifdefined\loesung \ifdefined\loesung
\textcolor{red}{
{\bf Solution}: Preorder: 5, 7, 1, 4, 2, 9; Inorder: 7, 1, 5, 2, 4, 9. {\bf Solution}: Preorder: 5, 7, 1, 4, 2, 9; Inorder: 7, 1, 5, 2, 4, 9.
Such traversals are implemented using a stack (explicitly or implicitly using Such traversals are implemented using a stack (explicitly or implicitly using
a recursive traversal)
a recursive traversal)}
\fi \fi
\subsection{Breadth-First-Search} \subsection{Breadth-First-Search}
What is the BFS traversal of the tree above? Which data structure is needed to implement What is the BFS traversal of the tree above? Which data structure is needed to implement
such a traversal? such a traversal?
\ifdefined\loesung \ifdefined\loesung
{\bf Solution}: BFS: 5, 7, 4, 1, 2, 9. You need a queue to implement BFS.
\textcolor{red}{
{\bf Solution}: BFS: 5, 7, 4, 1, 2, 9. You need a queue to implement BFS.}
\fi \fi
\section{Networking} \section{Networking}
\section{Regular Expressions and Shells} \section{Regular Expressions and Shells}
\subsection{Regular Expression}
Explain the following regex:
\begin{verbatim}
^(?:(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.){3}(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)$
\end{verbatim}
\ifdefined\loesung
\textcolor{red}{
{\bf Solution}: This regex describes well-formatted IPv4 addresses. Number of repetitions
given in braces, Question mark for optional choices, brackets denote ranges.}
\fi
\subsection{Extract Lines}
Write a shell command to extract lines number 101-110 from a file {\tt a.txt} and
output them (numerically sorted) to file {\tt b.txt}.
\ifdefined\loesung\textcolor{red}{
{\bf Solution}: {\tt cat a.txt | head -110 | tail -10 | sort -n > b.txt}}
\fi
\subsection{Large Files}
Write a shell command to find the file with the most number of lines in
the current directory.
\ifdefined\loesung\textcolor{red}{
{\bf Solution}: {\tt wc -l * | sort -nr} is key. One might get rid of the \emph{total} line count
and access the file name only. Optional.}
\fi
\section{Databases} \section{Databases}
%------------------------------------------------------------------------------ %------------------------------------------------------------------------------

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