_156topoSort2.java

import java.util.*;
public class _156topoSort2 {
    static class Edge{
        int src;
        int dest;
        public Edge(int s, int d){
            this.src=s;
            this.dest=d;
        }
    }
    static void createGraph(ArrayList<Edge>[] graph){
        for(int i=0;i<graph.length;i++){
            graph[i]=new ArrayList<>();
        }
        graph[2].add(new Edge(2,3));

        graph[3].add(new Edge(3,1));

        graph[4].add(new Edge(4,0));
        graph[4].add(new Edge(4,1));
        
        graph[5].add(new Edge(5,0));
        graph[5].add(new Edge(5,2));
    }
    public static void calcIndeg(ArrayList<Edge>[] graph,int indeg[]){
        for(int i= 0 ;i<graph.length;i++){
            int v=i;
            for(int j=0;j<graph[v].size();j++){
                Edge e = graph[v].get(j);
                indeg[e.dest]++;
            }
        }
    }
    public static void topSort(ArrayList<Edge>[] graph){
        int indeg[]=new int[graph.length];
        calcIndeg(graph, indeg);
        Queue<Integer> q = new LinkedList<>();
        for(int i = 0;i<indeg.length;i++){
            if(indeg[i]==0){
                q.add(i);
            }
        }
        while (!q.isEmpty()) {
            int curr=q.remove();
            System.out.print(curr +" ");
            for(int i = 0; i<graph[curr].size();i++){
                Edge e = graph[curr].get(i);
                indeg[e.dest]--;
                if(indeg[e.dest]==0){
                    q.add(e.dest);
                }
            }
        }
        System.out.println();
    }
    public static void main(String[] args) {
        int V = 6;
        @SuppressWarnings("unchecked")
        ArrayList<Edge> graph[] = new ArrayList[V];
        createGraph(graph);
        topSort(graph);
    }
}