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package algs42;
import stdlib.*;
import algs13.Stack;
/* ***********************************************************************
 *  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 final boolean[] marked;  // marked[v] = true if v is reachable from s
  private final 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<>();
    for (int x = v; x != s; x = edgeTo[x])
      path.push(x);
    path.push(s);
    return path;
  }

  public static void main(String[] args) {
    args = new String[] { "data/tinyDG.txt", "3" };

    In in = new In(args[0]);
    Digraph G = DigraphGenerator.fromIn(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.format("%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.format("%d to %d:  not connected\n", s, v);
      }

    }
  }

}