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\fnote{\copyright{} Christian Urban, King's College London, 2022}

Get familiar with constructing strings and printing strings

(i.e.~\texttt{println}, \texttt{mkString}, \texttt{toString}, \ldots)

\begin{lstlisting}[numbers=none]

\end{lstlisting}

Make sure you understand if-conditions in Scala: They are

\emph{expressions}, meaning they need to calculate a result. For

example an \texttt{if} without an else-branch is nearly always

\emph{not} what you intend to write (because you are not meant to

change any ``state'' outside the expression). Also, remember the quirks

in Scala with if-conditions needing parentheses and there is no

\texttt{then}-keyword.

\begin{lstlisting}[numbers=none]

scala> val s1 = "foo"

scala> val s2 = "bar"

scala  val s3 = "foobar"

scala> if (s1 == s2) print("equal") else print("unequal")

scala> if (s1 ++ s2 == s3) print("equal") else print("unequal")

\end{lstlisting}

Write \texttt{for}-comprehensions that enumerate all triples containing the numbers 1 - 5. That is,

print the list

\[

\texttt{(1,1,1)}, \texttt{(2,1,1)}, \texttt{(3,1,1)} \;\ldots\; \texttt{(5,5,5)}

\]

\noindent

Modify the \texttt{for}-comprehensions such that only triples are

printed where the sum is divisible by 3.  Then sort the list according

to the middle element (for this use \texttt{sortBy}).

Write a pretty print function for lists of integers which

``condenses'' elements in the list, meaning if there is a number

several times in a row, then print out \mbox{\texttt{n x e}}, where

\texttt{n} is the number of repetitions and \texttt{e} is the

number. For example

\begin{lstlisting}[numbers=none]

  List(1,1,1,2,3,3)    =>   List(3 x 1, 2, 2 x 3)

  List(1,2,3,4,4,4)    =>   List(1, 2, 3, 3 x 4)

  List(1,1,1,1,1,1)    =>   List(6 x 1)

  List(1,1,1,2,1,1)    =>   List(3 x 1, 2, 2 x 1)

\end{lstlisting}

You might like to define a separate function that first counts the occurences

for each element and returns a list of (Int, Int)-pairs .

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