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);
      }

    }
  }


}