regex questions added

gsd-questions.tex

@@ -93,9 +93,10 @@ Describe an algorithm to reverse a singly-linked list that \emph{does not}
 copy any memory cells.
 
 \ifdefined\loesung
+\textcolor{red}{
     {\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
-    as you you.
+    as you you.}
 \fi
 
 \subsection{Preorder Tree Traversal}
@@ -109,21 +110,49 @@ Consider the following tree and state the \emph{preorder} and \emph{inorder} tra
 \end{verbatim}
 Which data structure do you need to implement such a traversal?
 \ifdefined\loesung
+\textcolor{red}{
     {\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
-    a recursive traversal)
+    a recursive traversal)}
 \fi
 
 \subsection{Breadth-First-Search}
 What is the BFS traversal of the tree above? Which data structure is needed to implement
 such a traversal?
 \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
 
 \section{Networking}
 
 \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}
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