package algs42;
import stdlib.*;
import algs13.Queue;
import algs13.Stack;
/* ***********************************************************************
 *  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 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<>();
		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; // for BFS, mark as you enqueue
					q.enqueue(w);
				}
			}
		}
	}

	// BFS from multiple sources
	private void bfs(Digraph G, Iterable<Integer> sources) {
		Queue<Integer> q = new Queue<>();
		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<>();
		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) {
		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]);
		BreadthFirstDirectedPaths bfs = new BreadthFirstDirectedPaths(G, s);

		for (int v = 0; v < G.V(); v++) {
			if (bfs.hasPathTo(v)) {
				StdOut.format("%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.format("%d to %d (-):  not connected\n", s, v);
			}

		}
	}


}