Topological Sorting of a DAG

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https://www.geeksforgeeks.org/topological-sorting/

DFS based on Stack

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// A Java program to print topological sorting of a DAG 
// import java.util.*;
// This class represents a directed graph using adjacency list representation 
class Graph {
    // No. of vertices
    private int v;
    // Adjacency List as ArrayList of ArrayList's
    private ArrayList<Integer>[] adj;

    // Constructor
    Graph(int v) {
        this.v = v;
        adj = new ArrayList[this.v];
        for (int i = 0; i < this.v; ++i) adj[i]=new ArrayList<Integer>();
    }

    // Function to add an edge into the graph
    void addEdge(int v, int w) {
        adj[v].add(w);
    }

    // A recursive function used by topologicalSort
    void topologicalSortUtil(int v, boolean visited[], LinkedList<Integer> stack) {
        // Mark the current node as visited.
        visited[v] = true;
        Integer i;
        // Recur for all the vertices adjacent to thisvertex
        Iterator<Integer> it = adj[v].iterator();
        while (it.hasNext()) {
            i = it.next();
            if (!visited[i]) topologicalSortUtil(i, visited, stack);
        }
        // Push current vertex to stack which stores result
        stack.push(Integer.valueOf(v));
    }

    // The function to do Topological Sort. It uses recursive topologicalSortUtil()
    void topologicalSort() {
        LinkedList<Integer> stack = new LinkedList<Integer>();
        boolean visited[] = new boolean[this.v];
        // Call the recursive helper function to store Topological Sort starting from all vertices one by one
        for (int i = 0; i < this.v; i++){
            if (!visited[i]) topologicalSortUtil(i, visited, stack);
        }
        // Print contents of stack
        while (!stack.isEmpty()) System.out.print(stack.pop() + " ");
    }
}
/*
public class TS_GforG {
    // Driver method
    public static void main(String args[]) {
        // Create a graph given in the above diagram
        Graph g = new Graph(6);
        g.addEdge(5, 2);
        g.addEdge(5, 0);
        g.addEdge(4, 0);
        g.addEdge(4, 1);
        g.addEdge(2, 3);
        g.addEdge(3, 1);

        System.out.println("Topological sort of the given graph: ");
        g.topologicalSort();
        System.out.println();
    }
}*/

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