BF-UI.cpp

// A C++ program for Bellman-Ford's single source
// shortest path algorithm.
#include <iostream>

/*
                B   
            /  /\\ \
           A  / \\  E
            \/   \\ /
            C  -   D
*/

 
// a structure to represent a weighted edge in graph
struct Edge {
    int src, dest, weight;
};
 
// a structure to represent a connected, directed and
// weighted graph
struct Graph {
    // V-> Number of vertices, E-> Number of edges
    int V, E;
 
    // graph is represented as an array of edges.
    struct Edge* edge;
};
 
// Creates a graph with V vertices and E edges
struct Graph* createGraph(int V, int E)
{
    struct Graph* graph = new Graph;
    graph->V = V;
    graph->E = E;
    graph->edge = new Edge[E];
    return graph;
}
 
// A utility function used to print the solution
void printArr(int dist[], int n)
{
    printf("Vertex   Distance from Source\n");
    for (int i = 0; i < n; ++i)
        printf("%d \t\t %d\n", i, dist[i]);
}
 
// The main function that finds shortest distances from src
// to all other vertices using Bellman-Ford algorithm.  The
// function also detects negative weight cycle
void BellmanFord(struct Graph* graph, int src)
{
    int V = graph->V;
    int E = graph->E;
    int dist[V];
 
    // Step 1: Initialize distances from src to all other
    // vertices as INFINITE
    for (int i = 0; i < V; i++)
        dist[i] = INT_MAX;
    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 - 1; 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] != INT_MAX
                && dist[u] + weight < dist[v])
                dist[v] = dist[u] + weight;
        }
    }
 
    // Step 3: check for negative-weight cycles.  The above
    // step guarantees shortest distances if graph doesn't
    // contain negative weight cycle.  If we get a shorter
    // path, then there is a cycle.
    for (int i = 0; i < E; i++) {
        int u = graph->edge[i].src;
        int v = graph->edge[i].dest;
        int weight = graph->edge[i].weight;
        if (dist[u] != INT_MAX && dist[u] + weight < dist[v]) {
            printf("Graph contains negative weight cycle");
            return; // If negative cycle is detected, simply
                    // return
        }
    }
 
    printArr(dist, V);
 
    return;
}

void graphinput (int i, int a, int b,int w,struct Graph* graph){

    graph->edge[i].src = a;
    graph->edge[i].dest = b;
    graph->edge[i].weight = w;
    return;
} 

// Driver program to test above functions
int main()
{
    /* Let us create the graph given in above example */
    int V; // Number of vertices in graph 5
    printf("Number of vertices in graph: ");
    scanf("%d", &V);
    int E; // Number of edges in graph 8
    printf("Number of edges in graph: ");
    scanf("%d", &E);
    struct Graph* graph = createGraph(V, E);
 /*
    5
    8
    0 1 -1
    0 2 4
    1 2 3
    1 3 2
    1 4 2
    3 2 5 
    3 1 1
    4 3 -3
    // 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;
    */
   int a,b,w;
   for(int i=0;i<E;i++){
       
       printf("Enter %d edge source, Destination and Weight: " ,i);
       scanf("%d %d %d", &a, &b,&w);
    //    printf("Enter %d edge source:" ,i);
    //    scanf("%d",&a);
    //    printf("Enter %d edge source:", i);
    //    scanf("%d",&b);
    //    printf("Enter %d edge source:", i);
    //    scanf("%d",&w);
       graphinput(i,a,b,w,graph);
   }
 
    BellmanFord(graph, 0);
 
    return 0;
}