/*

* Sample usage: java BreadthFirstDirectedPaths tinyDG.txt 3

* Sample usage: java BreadthFirstDirectedPaths mediumDG.txt 3

*/

public class BreadthFirstDirectedPaths {

private boolean[] marked; // marked[v] = is there a shortest s-v path?

private int[] edgeTo; // last vertex on known path to this vertex

private final int s; // the source

public BreadthFirstDirectedPaths(Digraph G, int s){

marked = new boolean[G.V()];

edgeTo = new int[G.V()];

this.s = s;

bfs(G, s);

}

private void bfs(Digraph G, int s){

LinkedQueue<Integer> queue = new LinkedQueue<>();

marked[s] = true; // mark the source

queue.enqueue(s); // put source in the queue

while(!queue.isEmpty()){

int v = queue.dequeue(); // Remove the next vertex from the queue

for (int w : G.adj(v))

if (!marked[w]){ // For every unmarked adjacent vertex

edgeTo[w] = v; // save last edge on a shortest path

marked[w] = true;// mark it because path is known

queue.enqueue(w);// and add it to the queue

}

}

}

public boolean marked(int w){

return marked[w];

}

public boolean hasPathTo(int v){

return marked[v];

}

public Iterable<Integer> pathTo(int v){

if (!hasPathTo(v)) return null;

LinkedStack<Integer> path = new LinkedStack<>();

for (int x=v; x!=s; x=edgeTo[x])

path.push(x);

path.push(s);

return path;

}

public static void main(String[] args){

Digraph G = new Digraph(new In(args[0]));

int s = Integer.parseInt(args[1]);

BreadthFirstDirectedPaths bfs = new BreadthFirstDirectedPaths(G, s);

for (int v=0; v<G.V(); v++){

StdOut.print(s + " to " + v + ": ");

if (bfs.hasPathTo(v)){

for (int x: bfs.pathTo(v))

if (x==s) StdOut.print(x);

else StdOut.print("->"+x);

StdOut.println();

}

else StdOut.print("not connected\n");

}

}

}