Below is the syntax highlighted version of Graph.java
from §4.1 Undirected Graphs.
/****************************************************************************** * Compilation: javac Graph.java * Execution: java Graph input.txt * Dependencies: Bag.java Stack.java In.java StdOut.java * Data files: https://algs4.cs.princeton.edu/41graph/tinyG.txt * https://algs4.cs.princeton.edu/41graph/mediumG.txt * https://algs4.cs.princeton.edu/41graph/largeG.txt * * A graph, implemented using an array of sets. * Parallel edges and self-loops allowed. * * % java Graph tinyG.txt * 13 vertices, 13 edges * 0: 6 2 1 5 * 1: 0 * 2: 0 * 3: 5 4 * 4: 5 6 3 * 5: 3 4 0 * 6: 0 4 * 7: 8 * 8: 7 * 9: 11 10 12 * 10: 9 * 11: 9 12 * 12: 11 9 * * % java Graph mediumG.txt * 250 vertices, 1273 edges * 0: 225 222 211 209 204 202 191 176 163 160 149 114 97 80 68 59 58 49 44 24 15 * 1: 220 203 200 194 189 164 150 130 107 72 * 2: 141 110 108 86 79 51 42 18 14 * ... * ******************************************************************************/ import java.util.NoSuchElementException; /** * The {@code Graph} class represents an undirected graph of vertices * named 0 through <em>V</em> – 1. * It supports the following two primary operations: add an edge to the graph, * iterate over all of the vertices adjacent to a vertex. It also provides * methods for returning the degree of a vertex, the number of vertices * <em>V</em> in the graph, and the number of edges <em>E</em> in the graph. * Parallel edges and self-loops are permitted. * By convention, a self-loop <em>v</em>-<em>v</em> appears in the * adjacency list of <em>v</em> twice and contributes two to the degree * of <em>v</em>. * <p> * This implementation uses an <em>adjacency-lists representation</em>, which * is a vertex-indexed array of {@link Bag} objects. * It uses Θ(<em>E</em> + <em>V</em>) space, where <em>E</em> is * the number of edges and <em>V</em> is the number of vertices. * All instance methods take Θ(1) time. (Though, iterating over * the vertices returned by {@link #adj(int)} takes time proportional * to the degree of the vertex.) * Constructing an empty graph with <em>V</em> vertices takes * Θ(<em>V</em>) time; constructing a graph with <em>E</em> edges * and <em>V</em> vertices takes Θ(<em>E</em> + <em>V</em>) time. * <p> * For additional documentation, see * <a href="https://algs4.cs.princeton.edu/41graph">Section 4.1</a> * of <i>Algorithms, 4th Edition</i> by Robert Sedgewick and Kevin Wayne. * * @author Robert Sedgewick * @author Kevin Wayne */ public class Graph { private static final String NEWLINE = System.getProperty("line.separator"); private final int V; private int E; private Bag<Integer>[] adj; /** * Initializes an empty graph with {@code V} vertices and 0 edges. * param V the number of vertices * * @param V number of vertices * @throws IllegalArgumentException if {@code V < 0} */ public Graph(int V) { if (V < 0) throw new IllegalArgumentException("Number of vertices must be non-negative"); this.V = V; this.E = 0; adj = (Bag<Integer>[]) new Bag[V]; for (int v = 0; v < V; v++) { adj[v] = new Bag<Integer>(); } } /** * Initializes a graph from the specified input stream. * The format is the number of vertices <em>V</em>, * followed by the number of edges <em>E</em>, * followed by <em>E</em> pairs of vertices, with each entry separated by whitespace. * * @param in the input stream * @throws IllegalArgumentException if {@code in} is {@code null} * @throws IllegalArgumentException if the endpoints of any edge are not in prescribed range * @throws IllegalArgumentException if the number of vertices or edges is negative * @throws IllegalArgumentException if the input stream is in the wrong format */ public Graph(In in) { if (in == null) throw new IllegalArgumentException("argument is null"); try { this.V = in.readInt(); if (V < 0) throw new IllegalArgumentException("number of vertices in a Graph must be non-negative"); adj = (Bag<Integer>[]) new Bag[V]; for (int v = 0; v < V; v++) { adj[v] = new Bag<Integer>(); } int E = in.readInt(); if (E < 0) throw new IllegalArgumentException("number of edges in a Graph must be non-negative"); for (int i = 0; i < E; i++) { int v = in.readInt(); int w = in.readInt(); validateVertex(v); validateVertex(w); addEdge(v, w); } } catch (NoSuchElementException e) { throw new IllegalArgumentException("invalid input format in Graph constructor", e); } } /** * Initializes a new graph that is a deep copy of {@code G}. * * @param G the graph to copy * @throws IllegalArgumentException if {@code G} is {@code null} */ public Graph(Graph G) { this.V = G.V(); this.E = G.E(); if (V < 0) throw new IllegalArgumentException("Number of vertices must be non-negative"); // update adjacency lists adj = (Bag<Integer>[]) new Bag[V]; for (int v = 0; v < V; v++) { adj[v] = new Bag<Integer>(); } for (int v = 0; v < G.V(); v++) { // reverse so that adjacency list is in same order as original Stack<Integer> reverse = new Stack<Integer>(); for (int w : G.adj[v]) { reverse.push(w); } for (int w : reverse) { adj[v].add(w); } } } /** * Returns the number of vertices in this graph. * * @return the number of vertices in this graph */ public int V() { return V; } /** * Returns the number of edges in this graph. * * @return the number of edges in this graph */ public int E() { return E; } // throw an IllegalArgumentException unless {@code 0 <= v < V} private void validateVertex(int v) { if (v < 0 || v >= V) throw new IllegalArgumentException("vertex " + v + " is not between 0 and " + (V-1)); } /** * Adds the undirected edge v-w to this graph. * * @param v one vertex in the edge * @param w the other vertex in the edge * @throws IllegalArgumentException unless both {@code 0 <= v < V} and {@code 0 <= w < V} */ public void addEdge(int v, int w) { validateVertex(v); validateVertex(w); E++; adj[v].add(w); adj[w].add(v); } /** * Returns the vertices adjacent to vertex {@code v}. * * @param v the vertex * @return the vertices adjacent to vertex {@code v}, as an iterable * @throws IllegalArgumentException unless {@code 0 <= v < V} */ public Iterable<Integer> adj(int v) { validateVertex(v); return adj[v]; } /** * Returns the degree of vertex {@code v}. * * @param v the vertex * @return the degree of vertex {@code v} * @throws IllegalArgumentException unless {@code 0 <= v < V} */ public int degree(int v) { validateVertex(v); return adj[v].size(); } /** * Returns a string representation of this graph. * * @return the number of vertices <em>V</em>, followed by the number of edges <em>E</em>, * followed by the <em>V</em> adjacency lists */ public String toString() { StringBuilder s = new StringBuilder(); s.append(V + " vertices, " + E + " edges " + NEWLINE); for (int v = 0; v < V; v++) { s.append(v + ": "); for (int w : adj[v]) { s.append(w + " "); } s.append(NEWLINE); } return s.toString(); } /** * Unit tests the {@code Graph} data type. * * @param args the command-line arguments */ public static void main(String[] args) { In in = new In(args[0]); Graph G = new Graph(in); StdOut.println(G); } }