package algs41;
import stdlib.*;
import algs13.Stack;
/* ***********************************************************************
 *  Compilation:  javac DepthFirstPaths.java
 *  Execution:    java DepthFirstPaths G s
 *  Dependencies: Graph.java Stack.java StdOut.java
 *  Data files:   http://algs4.cs.princeton.edu/41undirected/tinyCG.txt
 *
 *  Run depth first search on an undirected graph.
 *  Runs in O(E + V) time.
 *
 *  %  java Graph tinyCG.txt
 *  6 8
 *  0: 2 1 5
 *  1: 0 2
 *  2: 0 1 3 4
 *  3: 5 4 2
 *  4: 3 2
 *  5: 3 0
 *
 *  % java DepthFirstPaths tinyCG.txt 0
 *  0 to 0:  0
 *  0 to 1:  0-2-1
 *  0 to 2:  0-2
 *  0 to 3:  0-2-3
 *  0 to 4:  0-2-3-4
 *  0 to 5:  0-2-3-5
 *
 *************************************************************************/

public class DepthFirstPaths {
  private final boolean[] marked; // marked[v] = is there an s-v path?
  private final int[] edgeTo;     // edgeTo[v] = last edge on s-v path
  private final int s;            // source vertex

  public DepthFirstPaths(Graph G, int s) {
    this.s = s;
    edgeTo = new int[G.V()];
    marked = new boolean[G.V()];
    dfsLoop (G, s);
  }

  // depth first search from v
  private void dfs(Graph G, int v) {
    //StdOut.format ("visited %d\n", v);
    marked[v] = true;
    for (int w : G.adj(v)) {
      if (!marked[w]) {
        edgeTo[w] = v;
        dfs(G, w);
      }
    }
  }
  private void dfsLoop(Graph G, int s) {
    Stack<Integer> stack = new Stack<>();
    stack.push(s);

    while (!stack.isEmpty()) {
      int v = stack.pop();
      marked[v] = true; // For DFS, mark as you pop
      for (int w : G.adj(v)) {
        if (!marked[w]) {
          edgeTo[w] = v;
          stack.push(w);
        }
      }
    }
  }
  private void dfsLoopReversed(Graph G, int s) {
    Stack<Integer> stack = new Stack<>();
    stack.push(s);

    while (!stack.isEmpty()) {
      int v = stack.pop();
      marked[v] = true;

      // tmp is used to get the vertices in the same order as used by the recursive version
      // tmp is not necessary, if you don't care about the order
      Stack<Integer> tmp = new Stack<>();
      for (int w : G.adj(v)) {
        if (!marked[w]) {
          edgeTo[w] = v;
          tmp.push(w);
        }
      }
      while (!tmp.isEmpty ())
        stack.push (tmp.pop ());
    }
  }



  // is there a path between s and w?
  public boolean hasPathTo(int w) {
    return marked[w];
  }

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

  public static void main(String[] args) {
    args = new String [] { "data/tinyG.txt", "0" };
    //args = new String [] { "data/tinyCG.txt", "0" };

    In in = new In(args[0]);
    Graph G = GraphGenerator.fromIn (in);
    StdOut.println (G);
    G.toGraphviz ("graph");

    int s = Integer.parseInt(args[1]);
    DepthFirstPaths dfs = new DepthFirstPaths(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);
      }

    }
  }

}