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);
			}

		}
	}

}