content: /*************************************************************************
   *  Compilation:  javac BreadthFirstDirectedPaths.java
   *  Execution:    java BreadthFirstDirectedPaths V E
   *  Dependencies: Digraph.java Queue.java Stack.java
   *
   *  Run breadth first search on a digraph.
   *  Runs in O(E + V) time.
   *
   *  % java BreadthFirstDirectedPaths tinyDG.txt 3
   *  3 to 0 (2):  3->2->0
   *  3 to 1 (3):  3->2->0->1
   *  3 to 2 (1):  3->2
   *  3 to 3 (0):  3
   *  3 to 4 (2):  3->5->4
   *  3 to 5 (1):  3->5
   *  3 to 6 (-):  not connected
   *  3 to 7 (-):  not connected
   *  3 to 8 (-):  not connected
   *  3 to 9 (-):  not connected
   *  3 to 10 (-):  not connected
   *  3 to 11 (-):  not connected
   *  3 to 12 (-):  not connected
   *
   *************************************************************************/
  
  public class BreadthFirstDirectedPaths {
      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
  
      // single source
      public BreadthFirstDirectedPaths(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;
          bfs(G, s);
      }
  
      // multiple sources
      public BreadthFirstDirectedPaths(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;
          bfs(G, sources);
      }
  
      // BFS from single source
      private void bfs(Digraph G, int s) {
          Queue<Integer> q = new Queue<Integer>();
          marked[s] = true;
          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;
                      q.enqueue(w);
                  }
              }
          }
      }
  
      // BFS from multiple sources
      private void bfs(Digraph G, Iterable<Integer> sources) {
          Queue<Integer> q = new Queue<Integer>();
          for (int s : sources) {
              marked[s] = true;
              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;
                      q.enqueue(w);
                  }
              }
          }
      }
  
      // length of shortest path from s (or sources) to v
      public int distTo(int v) {
          return distTo[v];
      }
  
      // is there a directed path from s (or sources) to v?
      public boolean hasPathTo(int v) {
          return marked[v];
      }
  
      // shortest path from s (or sources) to v; null if no such path
      public Iterable<Integer> pathTo(int 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;
      }
  
      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]);
          BreadthFirstDirectedPaths bfs = new BreadthFirstDirectedPaths(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);
              }
  
          }
      }
  
  
  }
  