DeluxeBFS.java

import edu.princeton.cs.algs4.Digraph;
import edu.princeton.cs.algs4.In;
import edu.princeton.cs.algs4.Queue;
import edu.princeton.cs.algs4.Stack;
import edu.princeton.cs.algs4.StdOut;

import java.util.TreeSet;

public class DeluxeBFS {
	private static final int INFINITY = Integer.MAX_VALUE;
	private boolean[] marked;  // marked[v] = is there an s->v path?
	private int[] edgeTo;      // edgeTo[v] = last edge on shortest s->v path
	private int[] distTo;      // distTo[v] = length of shortest s->v path
	private TreeSet<Integer> visit = new TreeSet<>();

	public DeluxeBFS(Digraph G, int s) {
		marked = new boolean[G.V()];
		distTo = new int[G.V()];
		edgeTo = new int[G.V()];
		for (int v = 0; v < G.V(); v++)
			distTo[v] = INFINITY;
		validateVertex(s);
		bfs(G, s);
	}

	public DeluxeBFS(Digraph G, Iterable<Integer> sources) {
		marked = new boolean[G.V()];
		distTo = new int[G.V()];
		edgeTo = new int[G.V()];
		for (int v = 0; v < G.V(); v++)
			distTo[v] = INFINITY;
		validateVertices(sources);
		bfs(G, sources);
	}

	private void bfs(Digraph G, int s) {
		Queue<Integer> q = new Queue<Integer>();
		marked[s] = true;
		visit.add(s);
		distTo[s] = 0;
		q.enqueue(s);
		while (!q.isEmpty()) {
			int v = q.dequeue();
			for (int w : G.adj(v)) {
				if (!marked[w]) {
					edgeTo[w] = v;
					distTo[w] = distTo[v] + 1;
					marked[w] = true;
					visit.add(w);
					q.enqueue(w);
				}
			}
		}
	}

	private void bfs(Digraph G, Iterable<Integer> sources) {
		Queue<Integer> q = new Queue<Integer>();
		for (int s : sources) {
			marked[s] = true;
			visit.add(s);
			distTo[s] = 0;
			q.enqueue(s);
		}
		while (!q.isEmpty()) {
			int v = q.dequeue();
			for (int w : G.adj(v)) {
				if (!marked[w]) {
					edgeTo[w] = v;
					distTo[w] = distTo[v] + 1;
					marked[w] = true;
					visit.add(w);
					q.enqueue(w);
				}
			}
		}
	}

	public boolean hasPathTo(int v) {
		validateVertex(v);
		return marked[v];
	}

	public int distTo(int v) {
		validateVertex(v);
		return distTo[v];
	}

	public Iterable<Integer> pathTo(int v) {
		validateVertex(v);

		if (!hasPathTo(v)) return null;
		Stack<Integer> path = new Stack<Integer>();
		int x;
		for (x = v; distTo[x] != 0; x = edgeTo[x])
			path.push(x);
		path.push(x);
		return path;
	}

	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));
	}

	private void validateVertices(Iterable<Integer> vertices) {
		if (vertices == null) {
			throw new IllegalArgumentException("argument is null");
		}
		int V = marked.length;
		for (int v : vertices) {
			if (v < 0 || v >= V) {
				throw new IllegalArgumentException("vertex " + v + " is not between 0 and " + (V-1));
			}
		}
	}

	public TreeSet<Integer> getVisit() {
		return visit;
	}

	public static void main(String[] args) {
		In in = new In(args[0]);
		Digraph G = new Digraph(in);
		// StdOut.println(G);

		int s = Integer.parseInt(args[1]);
		DeluxeBFS bfs = new DeluxeBFS(G, s);

		for (int v = 0; v < G.V(); v++) {
			if (bfs.hasPathTo(v)) {
				StdOut.printf("%d to %d (%d):  ", s, v, bfs.distTo(v));
				for (int x : bfs.pathTo(v)) {
					if (x == s) StdOut.print(x);
					else        StdOut.print("->" + x);
				}
				StdOut.println();
			}

			else {
				StdOut.printf("%d to %d (-):  not connected\n", s, v);
			}
		}
	}
}