public class GraphAdjacentMatrix_TopologicalSort_DFS {

    private boolean adjMatrix[][];
    private int numVertices;
    private boolean visited[];

    public GraphAdjacentMatrix_TopologicalSort_DFS(int numVertices) {
        this.numVertices = numVertices;
        adjMatrix = new boolean[numVertices][numVertices];
        visited = new boolean[numVertices];
    }

    public void setEdge(int i, int j) {
        adjMatrix[i][j] = true;
//        adjMatrix[j][i] = true; // directed
    }

    public void delEdge(int i, int j) {
        adjMatrix[i][j] = false;
//        adjMatrix[j][i] = false; // directed
    }

    public boolean isEdge(int i, int j) {
        return adjMatrix[i][j];
    }

    public int first(int v1){
        boolean[] ary = this.adjMatrix[v1];
        int firstNeighborIndex = this.numVertices; // return n if none
        for (int i = 0; i < ary.length; i++) {
            if (ary[i] != false){
                firstNeighborIndex = i;
                break;
            }
        }
        return firstNeighborIndex;
    }

    public int next(int v1, int v2){
        boolean[] ary = this.adjMatrix[v1];
        int nextNeighborIndex = this.numVertices; // return n if none
        for (int i = v2 + 1; i < ary.length; i++) {
            if (ary[i] != false){
                nextNeighborIndex = i;
                break;
            }
        }
        return nextNeighborIndex; // return n if none
    }

    public void topSort_DFS(int v){
        topSort_DFS(this.adjMatrix, v);
    }

    public void topSort_DFS(boolean[][] graph, int v){
        Previsit(graph, v);
        // mark the current node
        visited[v] = true;
        // find neighbor
        for (int nextV = this.first(v); nextV < this.numVertices; nextV = this.next(v, nextV)) {
            if (!visited[nextV]){
                topSort_DFS(graph, nextV);
            }
        }
        Postvisit(graph, v);
    }

    private void Previsit(boolean[][] graph, int v) {
//        System.out.println("Previsit: " + v); // do not print anything for topologicalSort implemented in DFS
    }

    private void Postvisit(boolean[][] graph, int v) {
        System.out.println("Postvisit: " + v); // we will get an reverse order
    }


    public String toString() {
        StringBuilder s = new StringBuilder();
        for (int i = 0; i < numVertices; i++) {
            s.append(i + ": ");
            for (boolean j : adjMatrix[i]) {
                s.append((j?1:0) + " ");
            }
            s.append("\n");
        }
        return s.toString();
    }

    public static void main(String[] args) {
        GraphAdjacentMatrix_TopologicalSort_DFS gam = new GraphAdjacentMatrix_TopologicalSort_DFS(8);

        // directed graph
        gam.setEdge(1, 2);
        gam.setEdge(1, 3);
        gam.setEdge(2, 6);
        gam.setEdge(2, 5);
        gam.setEdge(2, 4);
        gam.setEdge(3, 4);
        gam.setEdge(4, 5);
        gam.setEdge(5, 7);

        System.out.println("DFS: ");
        gam.topSort_DFS( 1);

        System.out.println();
    }

}