content: /*************************************************************************
   *  Compilation:  javac DepthFirstDirectedPaths.java
   *  Execution:    java DepthFirstDirectedPaths G s
   *  Dependencies: Digraph.java Stack.java
   *
   *  Determine reachability in a digraph from a given vertex using
   *  depth first search.
   *  Runs in O(E + V) time.
   *
   *  % tinyDG.txt 3
   *  3 to 0:  3-5-4-2-0
   *  3 to 1:  3-5-4-2-0-1
   *  3 to 2:  3-5-4-2
   *  3 to 3:  3
   *  3 to 4:  3-5-4
   *  3 to 5:  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 DepthFirstDirectedPaths {
      private boolean[] marked;  // marked[v] = true if v is reachable from s
      private int[] edgeTo;      // edgeTo[v] = last edge on path from s to v
      private final int s;       // source vertex
  
      // single source
      public DepthFirstDirectedPaths(Digraph G, int s) {
          marked = new boolean[G.V()];
          edgeTo = new int[G.V()];
          this.s = s;
          dfs(G, s);
      }
  
  
      private void dfs(Digraph G, int v) { 
          marked[v] = true;
          for (int w : G.adj(v)) {
              if (!marked[w]) {
                  edgeTo[w] = v;
                  dfs(G, w);
              }
          }
      }
  
      // is there a directed path from s to v?
      public boolean hasPathTo(int v) {
          return marked[v];
      }
  
      // return path from s to v; null if no such path
      public Iterable<Integer> pathTo(int v) {
          if (!hasPathTo(v)) return null;
          Stack<Integer> path = new Stack<Integer>();
          for (int x = v; x != s; x = edgeTo[x])
              path.push(x);
          path.push(s);
          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]);
          DepthFirstDirectedPaths dfs = new DepthFirstDirectedPaths(G, s);
  
          for (int v = 0; v < G.V(); v++) {
              if (dfs.hasPathTo(v)) {
                  StdOut.printf("%d to %d:  ", s, v);
                  for (int x : dfs.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);
              }
  
          }
      }
  
  }
  