Below is the syntax highlighted version of CC.java
from §4.1 Undirected Graphs.
/****************************************************************************** * Compilation: javac CC.java * Execution: java CC filename.txt * Dependencies: Graph.java StdOut.java Queue.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 * * Compute connected components using depth first search. * Runs in O(E + V) time. * * % java CC tinyG.txt * 3 components * 0 1 2 3 4 5 6 * 7 8 * 9 10 11 12 * * % java CC mediumG.txt * 1 components * 0 1 2 3 4 5 6 7 8 9 10 ... * * % java -Xss50m CC largeG.txt * 1 components * 0 1 2 3 4 5 6 7 8 9 10 ... * * Note: This implementation uses a recursive DFS. To avoid needing * a potentially very large stack size, replace with a nonrecursive * DFS ala NonrecursiveDFS.java. * ******************************************************************************/ /** * The {@code CC} class represents a data type for * determining the connected components in an undirected graph. * The <em>id</em> operation determines in which connected component * a given vertex lies; the <em>connected</em> operation * determines whether two vertices are in the same connected component; * the <em>count</em> operation determines the number of connected * components; and the <em>size</em> operation determines the number * of vertices in the connect component containing a given vertex. * <p> * The <em>component identifier</em> of a vertex is an integer between * 0 and <em>k</em>–1, where <em>k</em> is the number of connected components. * Two vertices have the same component identifier if and only if * they are in the same connected component. * <p> * This implementation uses depth-first search. * The constructor takes Θ(<em>V</em> + <em>E</em>) time, * where <em>V</em> is the number of vertices and <em>E</em> is the * number of edges. * Each instance method takes Θ(1) time. * It uses Θ(<em>V</em>) extra space (not including the graph). * <p> * For additional documentation, see * <a href="https://algs4.cs.princeton.edu/41graph">Section 4.1</a> * of <em>Algorithms, 4th Edition</em> by Robert Sedgewick and Kevin Wayne. * * @author Robert Sedgewick * @author Kevin Wayne */ public class CC { private boolean[] marked; // marked[v] = has vertex v been marked? private int[] id; // id[v] = id of connected component containing v private int[] size; // size[id] = number of vertices in given component private int count; // number of connected components /** * Computes the connected components of the undirected graph {@code G}. * * @param G the undirected graph */ public CC(Graph G) { marked = new boolean[G.V()]; id = new int[G.V()]; size = new int[G.V()]; for (int v = 0; v < G.V(); v++) { if (!marked[v]) { dfs(G, v); count++; } } } /** * Computes the connected components of the edge-weighted graph {@code G}. * * @param G the edge-weighted graph */ public CC(EdgeWeightedGraph G) { marked = new boolean[G.V()]; id = new int[G.V()]; size = new int[G.V()]; for (int v = 0; v < G.V(); v++) { if (!marked[v]) { dfs(G, v); count++; } } } // depth-first search for a Graph private void dfs(Graph G, int v) { marked[v] = true; id[v] = count; size[count]++; for (int w : G.adj(v)) { if (!marked[w]) { dfs(G, w); } } } // depth-first search for an EdgeWeightedGraph private void dfs(EdgeWeightedGraph G, int v) { marked[v] = true; id[v] = count; size[count]++; for (Edge e : G.adj(v)) { int w = e.other(v); if (!marked[w]) { dfs(G, w); } } } /** * Returns the component id of the connected component containing vertex {@code v}. * * @param v the vertex * @return the component id of the connected component containing vertex {@code v} * @throws IllegalArgumentException unless {@code 0 <= v < V} */ public int id(int v) { validateVertex(v); return id[v]; } /** * Returns the number of vertices in the connected component containing vertex {@code v}. * * @param v the vertex * @return the number of vertices in the connected component containing vertex {@code v} * @throws IllegalArgumentException unless {@code 0 <= v < V} */ public int size(int v) { validateVertex(v); return size[id[v]]; } /** * Returns the number of connected components in the graph {@code G}. * * @return the number of connected components in the graph {@code G} */ public int count() { return count; } /** * Returns true if vertices {@code v} and {@code w} are in the same * connected component. * * @param v one vertex * @param w the other vertex * @return {@code true} if vertices {@code v} and {@code w} are in the same * connected component; {@code false} otherwise * @throws IllegalArgumentException unless {@code 0 <= v < V} * @throws IllegalArgumentException unless {@code 0 <= w < V} */ public boolean connected(int v, int w) { validateVertex(v); validateVertex(w); return id(v) == id(w); } /** * Returns true if vertices {@code v} and {@code w} are in the same * connected component. * * @param v one vertex * @param w the other vertex * @return {@code true} if vertices {@code v} and {@code w} are in the same * connected component; {@code false} otherwise * @throws IllegalArgumentException unless {@code 0 <= v < V} * @throws IllegalArgumentException unless {@code 0 <= w < V} * @deprecated Replaced by {@link #connected(int, int)}. */ @Deprecated public boolean areConnected(int v, int w) { validateVertex(v); validateVertex(w); return id(v) == id(w); } // throw an IllegalArgumentException unless {@code 0 <= v < V} private void validateVertex(int v) { int V = marked.length; if (v < 0 || v >= V) throw new IllegalArgumentException("vertex " + v + " is not between 0 and " + (V-1)); } /** * Unit tests the {@code CC} 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); CC cc = new CC(G); // number of connected components int m = cc.count(); StdOut.println(m + " components"); // compute list of vertices in each connected component Queue<Integer>[] components = (Queue<Integer>[]) new Queue[m]; for (int i = 0; i < m; i++) { components[i] = new Queue<Integer>(); } for (int v = 0; v < G.V(); v++) { components[cc.id(v)].enqueue(v); } // print results for (int i = 0; i < m; i++) { for (int v : components[i]) { StdOut.print(v + " "); } StdOut.println(); } } }