diff -r 017f621f5835 -r 3ffe978a5664 cws/pre_cw02.tex --- a/cws/pre_cw02.tex Thu Nov 04 12:20:12 2021 +0000 +++ /dev/null Thu Jan 01 00:00:00 1970 +0000 @@ -1,161 +0,0 @@ -% !TEX program = xelatex -\documentclass{article} -\usepackage{../style} -\usepackage{disclaimer} -\usepackage{../langs} - -\begin{document} - - -%% should ask to lower case the words. - -\section*{Preliminary Part 2 (Scala, 3 Marks)} - -\mbox{}\hfill\textit{``What one programmer can do in one month,}\\ -\mbox{}\hfill\textit{two programmers can do in two months.''}\smallskip\\ -\mbox{}\hfill\textit{ --- Frederick P.~Brooks (author of The Mythical Man-Month)}\bigskip\medskip - -\IMPORTANT{You are asked to implement a Scala program for measuring similarity in - texts. The preliminary part is due on \cwSEVEN{} at 5pm and worth 3\%. - Any 1\% you achieve in the preliminary part counts as your ``weekly engagement''.} - -\noindent -Also note that the running time of each part will be restricted to a -maximum of 30 seconds on my laptop. - -\DISCLAIMER{} - - -\subsection*{Reference Implementation} - -Like the C++ part, the Scala part works like this: you -push your files to GitHub and receive (after sometimes a long delay) some -automated feedback. In the end we will take a snapshot of the submitted files and -apply an automated marking script to them.\medskip - -\noindent -In addition, the Scala part comes with reference -implementations in form of \texttt{jar}-files. This allows you to run -any test cases on your own computer. For example you can call Scala on -the command line with the option \texttt{-cp docdiff.jar} and then -query any function from the template file. Say you want to find out -what the function \texttt{occurrences} produces: for this you just need -to prefix it with the object name \texttt{CW7a}. If you want to find out what -these functions produce for the list \texttt{List("a", "b", "b")}, -you would type something like: - -\begin{lstlisting}[language={},numbers=none,basicstyle=\ttfamily\small] -$ scala -cp docdiff.jar - -scala> CW7a.occurrences(List("a", "b", "b")) -... -\end{lstlisting}%$ - -\subsection*{Hints} - -\noindent -\textbf{For the Preliminary Part:} useful operations involving regular -expressions: -\[\texttt{reg.findAllIn(s).toList}\] -\noindent finds all -substrings in \texttt{s} according to a regular regular expression -\texttt{reg}; useful list operations: \texttt{.distinct} -removing duplicates from a list, \texttt{.count} counts the number of -elements in a list that satisfy some condition, \texttt{.toMap} -transfers a list of pairs into a Map, \texttt{.sum} adds up a list of -integers, \texttt{.max} calculates the maximum of a list.\bigskip - - - -\newpage -\subsection*{Preliminary Part (3 Marks, file docdiff.scala)} - -It seems source code plagiarism---stealing and submitting someone -else's code---is a serious problem at other -universities.\footnote{Surely, King's students, after all their - instructions and warnings, would never commit such an offence. Yes?} -Detecting such plagiarism is time-consuming and disheartening for -lecturers at those universities. To aid these poor souls, let's -implement in this part a program that determines the similarity -between two documents (be they source code or texts in English). A -document will be represented as a list of strings. - - -\subsection*{Tasks} - -\begin{itemize} -\item[(1)] Implement a function that `cleans' a string by finding all - (proper) words in this string. For this use the regular expression - \texttt{\textbackslash{}w+} for recognising words and the library function - \texttt{findAllIn}. The function should return a document (a list of - strings).\\ - \mbox{}\hfill [0.5 Marks] - -\item[(2)] In order to compute the overlap between two documents, we - associate each document with a \texttt{Map}. This Map represents the - strings in a document and how many times these strings occur in the - document. A simple (though slightly inefficient) method for counting - the number of string-occurrences in a document is as follows: remove - all duplicates from the document; for each of these (unique) - strings, count how many times they occur in the original document. - Return a Map associating strings with occurrences. For example - - \begin{center} - \pcode{occurrences(List("a", "b", "b", "c", "d"))} - \end{center} - - produces \pcode{Map(a -> 1, b -> 2, c -> 1, d -> 1)} and - - \begin{center} - \pcode{occurrences(List("d", "b", "d", "b", "d"))} - \end{center} - - produces \pcode{Map(d -> 3, b -> 2)}.\hfill[1 Mark] - -\item[(3)] You can think of the Maps calculated under (2) as memory-efficient - representations of sparse ``vectors''. In this subtask you need to - implement the \emph{product} of two such vectors, sometimes also called - \emph{dot product} of two vectors.\footnote{\url{https://en.wikipedia.org/wiki/Dot_product}} - - For this dot product, implement a function that takes two documents - (\texttt{List[String]}) as arguments. The function first calculates - the (unique) strings in both. For each string, it multiplies the - corresponding occurrences in each document. If a string does not - occur in one of the documents, then the product for this string is zero. At the end - you need to add up all products. For the two documents in (2) the dot - product is 7, because - - \[ - \underbrace{1 * 0}_{"a"} \;\;+\;\; - \underbrace{2 * 2}_{"b"} \;\;+\;\; - \underbrace{1 * 0}_{"c"} \;\;+\;\; - \underbrace{1 * 3}_{"d"} \qquad = 7 - \] - - \hfill\mbox{[1 Mark]} - -\item[(4)] Implement first a function that calculates the overlap - between two documents, say $d_1$ and $d_2$, according to the formula - - \[ - \texttt{overlap}(d_1, d_2) = \frac{d_1 \cdot d_2}{max(d_1^2, d_2^2)} - \] - - where $d_1^2$ means $d_1 \cdot d_1$ and so on. - You can expect this function to return a \texttt{Double} between 0 and 1. The - overlap between the lists in (2) is $0.5384615384615384$. - - Second, implement a function that calculates the similarity of - two strings, by first extracting the substrings using the clean - function from (1) - and then calculating the overlap of the resulting documents.\\ - \mbox{}\hfill\mbox{[0.5 Marks]} -\end{itemize} - - -\end{document} - -%%% Local Variables: -%%% mode: latex -%%% TeX-master: t -%%% End: