package graphs.digraphs;
import java.util.Queue;
import java.util.LinkedList;
import java.util.Stack;

/*************************************************************************
 *  Run breadth first search on a digraph.
 */
public class DiGraphBFSPath {
	private static final int INFINITY = Integer.MAX_VALUE;
    private boolean[] visited;  // visited[v] = is there an s-v path?
    private int[] distTo;      // distTo[v] = length of shortest s-v path
    private int[] edgeTo;      // edgeTo[v] = last edge on shortest s-v path
    private final int s;       // the source

    public DiGraphBFSPath(DiGraph G, int s) {
        this.s = s;
        visited = new boolean[G.numberOfVerteces()];
        distTo = new int[G.numberOfVerteces()];
        edgeTo = new int[G.numberOfVerteces()];
        for (int v = 0; v < G.numberOfVerteces(); v++) distTo[v] = INFINITY;
        distTo[s] = 0;
        visited[s] = true;
        bfs(G, s);
    }

    private void bfs(DiGraph G, int s) {
        Queue<Integer> q = new LinkedList<Integer>();
        q.add(s);
        while (!q.isEmpty()) {
            int v = q.poll();
            for (int w : G.adjacents(v)) {
                if (!visited[w]) {
                    q.add(w);
                    edgeTo[w] = v;
                    distTo[w] = distTo[v] + 1;
                    visited[w] = true;
                }
            }
        }
    }

    // length of shortest path from s to v
    public int distanceTo(int v) {
        return distTo[v];
    }

    // is there a directed path from s to v?
    public boolean hasPathTo(int v) {
        return visited[v];
    }

    // return shortest path from s to v; null if no such path
    public Iterable<Integer> pathTo(int v) {
        if (!hasPathTo(v)) return null;
        Stack<Integer> stack = new Stack<Integer>();
        for (int x = v; x != s; x = edgeTo[x])
            stack.push(x);
        stack.push(s);
        return stack;
    }


}