Bellman-Ford.java

import java.util.*;
public class BellmanFord
{
    public static long dist[];
    public static long prev[];
    public static LinkedList<DirectedEdge> edgesList = new LinkedList<DirectedEdge>();
    
    public static class DirectedEdge{
        protected int v; 
        protected int w; // edge
        protected int weight; // weight;
        
        public DirectedEdge(int v, int w, int weight){
            this.v = v;
            this.w = w;
            this.weight = weight;
        }
        
        public int from(){
            return v;
        }
        
        public int to(){
            return w;
        }
        
        public int weight(){
            return weight;
        }
        
        
        public String toString(){
            return v + "->" + w + " " + String.format("%d", weight);
        }
        
    }
    
    public static class WeightableDiGraph{
        protected int V; //vertex;
        protected int E; //edges;
        protected ArrayList<DirectedEdge>[] adj;
        
        
        
        
        public WeightableDiGraph(int V){
            this.V = V;
            this.E = 0;
            adj = (ArrayList<DirectedEdge>[]) new ArrayList[V];
            for (int v = 0; v < V; v++) {
                adj[v] = new ArrayList<DirectedEdge>();
            }
            
        }
        public int V(){
            return this.V;
        }
        
        public int E(){
            return this.E;
        }
        
        
        public void addEdge(int v, int w, int weight){
            this.E++;
            DirectedEdge item = new DirectedEdge(v, w, weight);
            adj[v].add(item);
            edgesList.add(item);
        }
        
        public String toString() {
            StringBuilder s = new StringBuilder();
            String NEWLINE = System.getProperty("line.separator");
            s.append(V + " vertices, " + E + " edges " + NEWLINE);
            for (int v = 0; v < V; v++) {
                s.append(String.format("%d: ", v));
                for (DirectedEdge e : adj[v]) {
                    s.append(e + "  ");
                }
                s.append(NEWLINE);
            }
            return s.toString();
        }
        public Iterable<DirectedEdge> adj(int v) {
            if (v < 0 || v >= V) throw new IndexOutOfBoundsException();
            return this.adj[v];
        }
        
    }
    
   
    
    
    public static int BellmanFord(WeightableDiGraph g){
        Arrays.fill(dist, Long.MAX_VALUE);
        Arrays.fill(prev, -1);
        dist[0] = 0;
        for(int i = 1; i < g.V() - 1; i++){
            for(DirectedEdge e : g.adj(i)){
                
                if(dist[e.to()] > dist[e.from()] + e.weight()){
                    dist[e.to()] = dist[e.from()] + e.weight();
                    prev[e.to()] = e.to();
                }
            }
        }
        
        for(int i = 0; i < g.V(); i++){
            for(DirectedEdge e : g.adj(i)){
                if(dist[e.to()] > dist[e.from()] + e.weight())
                    return 1;
            }
        }
        return 0;
    }
   
    public static void main(String args[]){
        int n, m, v, w, weight;
        Scanner sc = new Scanner(System.in);
        n = sc.nextInt();
        m = sc.nextInt();
        dist = new long[n];
        prev = new long[n];
        WeightableDiGraph g = new WeightableDiGraph(n);
        for(int i = 0; i < m; i++){
            v = sc.nextInt();
            w = sc.nextInt();
            weight = sc.nextInt();
            g.addEdge(v - 1, w - 1, weight);
        }

        System.out.println(BellmanFord(g));
    }
}



/**
*
* Sample Input:
* 4 4
* 1 2 1
* 4 1 2
* 2 3 2
* 3 1 -5
* Sample Output:
* 1
*
*
*/

In BellmanFord method you only iterate through the adjacent vertexes of current vertex.However at each iteration you must iterate through all edges.You need to add one for loop before for(DşrectedEdge e:g.adj()) that goes from 0 to V-1.In that case the running time will become v^2+ve which can be also optimized by storing edges in a list etc.