content: /*************************************************************************
   *  Compilation:  javac DepthFirstPaths.java
   *  Execution:    java DepthFirstPaths G s
   *  Dependencies: Graph.java Stack.java StdOut.java
   *  Data files:   http://algs4.cs.princeton.edu/41undirected/tinyCG.txt
   *
   *  Run depth first search on an undirected graph.
   *  Runs in O(E + V) time.
   *
   *  %  java Graph tinyCG.txt
   *  6 8
   *  0: 2 1 5 
   *  1: 0 2 
   *  2: 0 1 3 4 
   *  3: 5 4 2 
   *  4: 3 2 
   *  5: 3 0 
   *
   *  % java DepthFirstPaths tinyCG.txt 0
   *  0 to 0:  0
   *  0 to 1:  0-2-1
   *  0 to 2:  0-2
   *  0 to 3:  0-2-3
   *  0 to 4:  0-2-3-4
   *  0 to 5:  0-2-3-5
   *
   *************************************************************************/
  
  public class DepthFirstPaths {
      private boolean[] marked;    // marked[v] = is there an s-v path?
      private int[] edgeTo;        // edgeTo[v] = last edge on s-v path
      private final int s;         // source vertex
  
      public DepthFirstPaths(Graph G, int s) {
          this.s = s;
          edgeTo = new int[G.V()];
          marked = new boolean[G.V()];
          dfs(G, s);
      }
  
      // depth first search from v
      private void dfs(Graph G, int v) {
          marked[v] = true;
          for (int w : G.adj(v)) {
              if (!marked[w]) {
                  edgeTo[w] = v;
                  dfs(G, w);
              }
          }
      }
  
      // is there a path between s and v?
      public boolean hasPathTo(int v) {
          return marked[v];
      }
  
      // return a path between 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]);
          Graph G = new Graph(in);
          int s = Integer.parseInt(args[1]);
          DepthFirstPaths dfs = new DepthFirstPaths(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);
              }
  
          }
      }
  
  }
  