% https://git.betalupi.com/Mark/latex-packages
% use [nosolutions] flag to hide solutions.
% use [solutions] flag to show solutions.
% Last built with version 1.1.0
\documentclass[
	solutions
]{ormc_handout}

\usepackage{subfiles}
\usetikzlibrary{arrows.meta}
\usetikzlibrary{shapes.geometric}

% We put nodes in a separate layer, so we can
% slightly overlap with paths for a perfect fit
\pgfdeclarelayer{nodes}
\pgfdeclarelayer{path}
\pgfsetlayers{main,nodes}

% Layer settings
\tikzset{
	% Layer hack, lets us write
	% later = * in scopes.
	layer/.style = {
		execute at begin scope={\pgfonlayer{#1}},
		execute at end scope={\endpgfonlayer}
	},
	%
	% Arrowhead tweaks
	>={Latex[ width=2mm, length=2mm ]},
	label/.style = {
		circle,
		% For automatic red background in solutions
		fill = \ORMCbgcolor,
		draw = none
	},
	%
	% Nodes
	main/.style = {
		draw,
		circle,
		fill = white
	},
	%
	% Flow annotations
	flow/.style = {
		opacity = 1,
		thin,
		inner xsep = 2.5mm,
		inner ysep = 2.5mm
	},
	%
	% Paths
	path/.style = {
		line width = 4mm,
		draw = black,
		% Lengthen paths so they're
		% completely under nodes.
		line cap = rect,
		opacity = 0.3
	}
}

\begin{document}

	\maketitle
		<Advanced 2>
		<Fall 2022>
		{Algorithms on Graphs: Flow}
		{Prepared by Mark on \today}


	\subfile{parts/00 review}
	\subfile{parts/01 flow}
	\subfile{parts/02 residual}
	\subfile{parts/03 fulkerson}





	\problem{Maximum Cardinality Matching}

	A \textit{matching} is a subset of edges in a bipartite graph. Nodes in a matching must not have more than one edge connected to them. \\
	A matching is \textit{maximal} if it has more edges than any other matching.

	\vspace{5mm}

	\begin{minipage}[t]{0.48\textwidth}
	\begin{center}
		Initial Graph \\
		\vspace{2mm}
		\begin{tikzpicture}
			% Nodes
			\begin{scope}[layer = nodes]
				\node[main] (A1) at (0mm, 24mm) {};
				\node[main] (A2) at (0mm, 18mm) {};
				\node[main] (A3) at (0mm, 12mm) {};
				\node[main] (A4) at (0mm, 6mm) {};
				\node[main] (A5) at (0mm, 0mm) {};
				\node[main] (B1) at (20mm, 24mm) {};
				\node[main] (B2) at (20mm, 18mm) {};
				\node[main] (B3) at (20mm, 12mm) {};
				\node[main] (B4) at (20mm, 6mm) {};
				\node[main] (B5) at (20mm, 0mm) {};
			\end{scope}

			% Edges
			\draw
				(A1) edge (B2)
				(A1) edge (B3)
				(A2) edge (B1)
				(A2) edge (B4)
				(A4) edge (B3)
				(A2) edge (B3)
				(A5) edge (B3)
				(A5) edge (B4)
			;

		\end{tikzpicture}
	\end{center}
	\end{minipage}
	\hfill
	\begin{minipage}[t]{0.48\textwidth}
	\begin{center}
		Maximal Matching \\
		\vspace{2mm}
		\begin{tikzpicture}
			% Nodes
			\begin{scope}[layer = nodes]
				\node[main] (A1) at (0mm, 24mm) {};
				\node[main] (A2) at (0mm, 18mm) {};
				\node[main] (A3) at (0mm, 12mm) {};
				\node[main] (A4) at (0mm, 6mm) {};
				\node[main] (A5) at (0mm, 0mm) {};
				\node[main] (B1) at (20mm, 24mm) {};
				\node[main] (B2) at (20mm, 18mm) {};
				\node[main] (B3) at (20mm, 12mm) {};
				\node[main] (B4) at (20mm, 6mm) {};
				\node[main] (B5) at (20mm, 0mm) {};
			\end{scope}

			% Edges
			\draw[opacity = 0.4]
				(A1) edge (B2)
				(A1) edge (B3)
				(A2) edge (B1)
				(A2) edge (B4)
				(A4) edge (B3)
				(A4) edge (B3)
				(A5) edge (B3)
				(A5) edge (B4)
			;
			\draw
				(A1) edge (B2)
				(A2) edge (B1)
				(A4) edge (B3)
				(A5) edge (B4)
			;
		\end{tikzpicture}
	\end{center}
	\end{minipage}

	\vspace{5mm}

	Devise an algorithm to find a maximal matching in any bipartite graph. \\
	Find an upper bound for its runtime.

	\begin{solution}
		Turn this into a maximum flow problem and use FF. \\
		Connect a node $S$ to all nodes in the left group and a node $T$ to all nodes in the right group. All edges have capacity 1.

		\vspace{2ex}

		Just like FF, this algorithm will take at most $\min(\# \text{ left nodes}, \# \text{ right nodes})$ iterations.
	\end{solution}

\end{document}