#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <limits.h>
struct Edge
{
// This structure is equal to an edge. Edge contains two end points. These edges are directed edges so they
//contain source and destination and some weight. These 3 are elements in this structure
int source, destination, weight;
};
// a structure to represent a connected, directed and weighted graph
struct Graph
{
int V, E;
// V is number of vertices and E is number of edges
struct Edge* edge;
// This structure contain another structure which we already created edge.
};
struct Graph* createGraph(int V, int E)
{
struct Graph* graph = (struct Graph*) malloc( sizeof(struct Graph));
//Allocating space to structure graph
graph->V = V; //assigning values to structure elements that taken form user.
graph->E = E;
graph->edge = (struct Edge*) malloc( graph->E * sizeof( struct Edge ) );
//Creating "Edge" type structures inside "Graph" structure, the number of edge type structures are equal to number of edges
return graph;
}
void FinalSolution(int dist[], int n)
{
// This function prints the final solution
printf("\nVertex\tDistance from Source Vertex\n");
int i;
for (i = 0; i < n; ++i){
printf("%d \t\t %d\n", i, dist[i]);
}
}
void BellmanFord(struct Graph* graph, int source)
{
int V = graph->V;
int E = graph->E;
int StoreDistance[V];
int i,j;
// This is initial step that we know , we initialize all distance to infinity except source.
// We assign source distance as 0(zero)
for (i = 0; i < V; i++)
StoreDistance[i] = INT_MAX;
StoreDistance[source] = 0;
//The shortest path of graph that contain V vertices, never contain "V-1" edges. So we do here "V-1" relaxations
for (i = 1; i <= V-1; i++)
{
for (j = 0; j < E; j++)
{
int u = graph->edge[j].source;
int v = graph->edge[j].destination;
int weight = graph->edge[j].weight;
if (StoreDistance[u] + weight < StoreDistance[v])
StoreDistance[v] = StoreDistance[u] + weight;
}
}
// Actually upto now shortest path found. But BellmanFord checks for negative edge cycle. In this step we check for that
// shortest distances if graph doesn't contain negative weight cycle.
// If we get a shorter path, then there is a negative edge cycle.
for (i = 0; i < E; i++)
{
int u = graph->edge[i].source;
int v = graph->edge[i].destination;
int weight = graph->edge[i].weight;
if (StoreDistance[u] + weight < StoreDistance[v])
printf("This graph contains negative edge cycle\n");
}
FinalSolution(StoreDistance, V);
return;
}
int main()
{
int V,E,S; //V = no.of Vertices, E = no.of Edges, S is source vertex
printf("Enter number of vertices in graph\n");
scanf("%d",&V);
printf("Enter number of edges in graph\n");
scanf("%d",&E);
printf("Enter your source vertex number\n");
scanf("%d",&S);
struct Graph* graph = createGraph(V, E); //calling the function to allocate space to these many vertices and edges
int i;
for(i=0;i<E;i++){
printf("\nEnter edge %d properties Source, destination, weight respectively\n",i+1);
scanf("%d",&graph->edge[i].source);
scanf("%d",&graph->edge[i].destination);
scanf("%d",&graph->edge[i].weight);
}
BellmanFord(graph, S);
//passing created graph and source vertex to BellmanFord Algorithm function
return 0;
}
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