Added regex handout

Misc/Warm-Ups/regex.tex

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+% use [nosolutions] flag to hide solutions.
+% use [solutions] flag to show solutions.
+\documentclass[
+	nosolutions
+]{../../resources/ormc_handout}
+
+
+\usepackage{xcolor}
+\usepackage{soul}
+
+\definecolor{Light}{gray}{.90}
+\sethlcolor{Light}
+\newcommand{\htexttt}[1]{\texttt{\hl{#1}}}
+
+\begin{document}
+
+	\maketitle
+		{The Regex Warm-Up}
+		{Prepared by Mark on \today}
+
+	Yesterday we discussed Deterministic Finite Automata. One interesting application of these mathematical objects is pattern matching, usually in the form of Regular Expressions. \\
+	(abbreviated \say{regex}, which is pronounced like \say{gif})
+
+	\vspace{2mm}
+
+	Regex is a language used to specify patterns in a string. You can think it as a concise way to define a DFA, using text instead of a huge graph. \\
+
+	Often enough, a clever regex pattern can do the work of a few hundred lines of code. \\
+
+	\vspace{2mm}
+
+	Like the DFAs we have studied, a regex pattern \textit{accepts} or \textit{rejects} a string. However, we don't usually use this terminology when discussing regex, instead opting to say a pattern \textit{matches} or \textit{doesn't match} a string. \\
+
+	\vspace{5mm}
+
+	\textbf{Quantifiers} \\
+	Quantifiers tell us how many of a character to match. \\
+	There are four of them:
+	\htexttt{+}, \htexttt{*}, \htexttt{?}, and \htexttt{\{ \}}
+
+	\vspace{2mm}
+
+	\htexttt{+} means \say{match one or more of the preceding token} \\
+	\htexttt{*} means \say{match zero or more of the preceding token} \\
+
+	For example, the pattern \htexttt{ca+t} will match the following strings:
+	\begin{itemize}
+		\item \texttt{cat}
+		\item \texttt{caat}
+		\item \texttt{caaaaaaaat}
+	\end{itemize}
+	\htexttt{ca+t} will \textbf{not} match the string \texttt{ct}. \\
+	The pattern \htexttt{ca*t} will match all the strings above, including \texttt{ct}.
+	\vspace{2mm}
+
+
+	\htexttt{?} means \say{match one or none of the preceeding token} \\
+	The pattern \htexttt{linea?r} will match only \texttt{linear} and \texttt{liner} \\
+	\vspace{2mm}
+
+	Patterns with brackets \htexttt{\{min, max\}} are the most flexible quantifier. \\
+	They specify exactly how many tokens to match: \\
+	\htexttt{ab\{2\}a} will match only \texttt{abba}. \\
+	\htexttt{ab\{1,3\}a} will match \texttt{aba}, \texttt{abba}, \texttt{abbba}. \\
+	\htexttt{ab\{2,\}a} will match any \texttt{ab...ba} with at least two \texttt{b}s.
+
+	\vspace{5mm}
+
+	\problem{}
+	Write the patterns \htexttt{a*} and \htexttt{a+} using only \htexttt{\{ \}}.
+	\vfill
+
+	\problem{}
+	Draw a DFA equivalent to the regex pattern \htexttt{01*0}.
+	\vfill
+
+	\pagebreak
+
+
+
+
+
+
+	\textbf{Characters, Sets, and Groups}
+
+	Characters tell us what to match.
+
+	Usually we specify them literally, as shown above: \\
+	\texttt{a+} means \say{one or more \texttt{a} character} \\
+
+	\vspace{2mm}
+
+	There are, however, other ways we can specify characters. \\
+
+	\vspace{2mm}
+
+	The first such way is the \textit{set}, denoted \htexttt{[ ]}. A set can pretend to be any character inside it. \\
+	For example, \htexttt{m[aoy]th} will match \texttt{math}, \texttt{moth}, or \texttt{myth}. \\
+	\htexttt{a[01]+b} will match \texttt{a0b}, \texttt{a111b}, \texttt{a1100110b}, and any other similar string. \\
+
+	\vspace{2mm}
+
+	If we want to keep characters together, we can use the \textit{group}, denoted \htexttt{( )}. \\
+
+	Groups work exactly as you'd expect, representing an atomic\footnotemark{} group of characters. \\
+	\htexttt{a(01)+b} will match \texttt{a01b} and \texttt{a010101b}, but will \textbf{not} match \texttt{a0b}, \texttt{a1b}, or \texttt{a1100110b}. \\
+
+	\footnotetext{In other words, \say{unbreakable}}
+
+
+	\problem{}<regex>
+	You are now familiar with most of the tools regex has to offer. \\
+	Match the following strings:
+	\begin{enumerate}
+		\item An ISO-8601 date, like \texttt{2022-10-29}. \\
+		Invalid dates like \texttt{2022-13-29} should also be matched. \\
+
+		\item A hexadecimal integer of any length.
+		\item A UCLA room number, like \texttt{MS 5118} or \texttt{Kinsey 1220B}
+		\item Any ISBN-10 of the form \texttt{0-316-00395-7}. \\
+		Remember that the check digit can be an \texttt{X}. \\
+		Dashes are optional.
+	\end{enumerate}
+
+
+
+	\vfill
+
+
+
+
+
+	\problem{}
+	If you'd like to know more, check out \texttt{regexr.com}. There's an interative regex prompt that provices explanations, as well as a cheatsheet that explains every regex token there is. You can find a nice set of challenges at \texttt{http://regex.alf.nu} \\
+	I especially encourage you to look into this if you are interested in computer science.
+	\pagebreak
+
+	\problem{}
+	Draw a DFA for each of the following regex strings. \\
+	\begin{itemize}
+		\item Your solution to \ref{regex}, Part 2
+		\item Your solution to \ref{regex}, Part 3
+		\item Your solution to \ref{regex}, Part 4
+	\end{itemize}
+\end{document}