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Create BellmanFordAlgorithm.java #98

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124 changes: 124 additions & 0 deletions dynamic-programming/BellmanFordAlgorithm.java
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import java.io.*;
import java.lang.*;
import java.util.*;
class Graph {

// A class to represent a weighted edge in graph
class Edge {
int src, dest, weight;
Edge() { src = dest = weight = 0; }
};

int V, E;
Edge edge[];

// Creates a graph with V vertices and E edges
Graph(int v, int e)
{
V = v;
E = e;
edge = new Edge[e];
for (int i = 0; i < e; ++i)
edge[i] = new Edge();
}

void BellmanFord(Graph graph, int src)
{
int V = graph.V, E = graph.E;
int dist[] = new int[V];

// Step 1: Initialize distances from src to all
// other vertices as INFINITE
for (int i = 0; i < V; ++i)
dist[i] = Integer.MAX_VALUE;
dist[src] = 0;

// Step 2: Relax all edges |V| - 1 times. A simple
// shortest path from src to any other vertex can
// have at-most |V| - 1 edges
for (int i = 1; i < V; ++i) {
for (int j = 0; j < E; ++j) {
int u = graph.edge[j].src;
int v = graph.edge[j].dest;
int weight = graph.edge[j].weight;
if (dist[u] != Integer.MAX_VALUE
&& dist[u] + weight < dist[v])
dist[v] = dist[u] + weight;
}
}

for (int j = 0; j < E; ++j) {
int u = graph.edge[j].src;
int v = graph.edge[j].dest;
int weight = graph.edge[j].weight;
if (dist[u] != Integer.MAX_VALUE
&& dist[u] + weight < dist[v]) {
System.out.println(
"Graph contains negative weight cycle");
return;
}
}
printArr(dist, V);
}


void printArr(int dist[], int V)
{
System.out.println("Vertex Distance from Source");
for (int i = 0; i < V; ++i)
System.out.println(i + "\t\t" + dist[i]);
}

// Driver's code
public static void main(String[] args)
{
int V = 5; // Number of vertices in graph
int E = 8; // Number of edges in graph

Graph graph = new Graph(V, E);

// add edge 0-1 (or A-B in above figure)
graph.edge[0].src = 0;
graph.edge[0].dest = 1;
graph.edge[0].weight = -1;

// add edge 0-2 (or A-C in above figure)
graph.edge[1].src = 0;
graph.edge[1].dest = 2;
graph.edge[1].weight = 4;

// add edge 1-2 (or B-C in above figure)
graph.edge[2].src = 1;
graph.edge[2].dest = 2;
graph.edge[2].weight = 3;

// add edge 1-3 (or B-D in above figure)
graph.edge[3].src = 1;
graph.edge[3].dest = 3;
graph.edge[3].weight = 2;

// add edge 1-4 (or B-E in above figure)
graph.edge[4].src = 1;
graph.edge[4].dest = 4;
graph.edge[4].weight = 2;

// add edge 3-2 (or D-C in above figure)
graph.edge[5].src = 3;
graph.edge[5].dest = 2;
graph.edge[5].weight = 5;

// add edge 3-1 (or D-B in above figure)
graph.edge[6].src = 3;
graph.edge[6].dest = 1;
graph.edge[6].weight = 1;

// add edge 4-3 (or E-D in above figure)
graph.edge[7].src = 4;
graph.edge[7].dest = 3;
graph.edge[7].weight = -3;

// Function call
graph.BellmanFord(graph, 0);
}
}