added bellman-ford for c++ (#115)

graphs/README.md

@@ -3,5 +3,4 @@
 ### C or C++
 
 1. [Kruskal Algorithm](c-or-cpp/kruskal-algorithm.cpp)
-
+2. [Bellman Ford Algorithm](c-or-cpp/bellman-ford.cpp)
-

graphs/c-or-cpp/bellman-ford.cpp

@@ -0,0 +1,92 @@
+//Bellman Ford Algorithm
+#include<bits/stdc++.h>
+using namespace std;
+
+
+bool bellman_ford(vector<tuple<int,int,int>>graph,int V,int s,vector<int>&dist)
+{
+
+	//no. of edges
+	int n = graph.size();
+	for(int i=0;i<V;i++)
+	{
+		dist.push_back(INT_MAX);
+	}
+
+	dist[s] = 0;
+
+	//V-1 times relaxation of all edges is done
+	for(int i=0;i<V-1;i++)
+	{
+		for(int j=0;j<n;j++)
+		{
+			int src = get<0>(graph[j]);
+			int dest = get<1>(graph[j]);
+			int weight = get<2>(graph[j]);
+
+			if(dist[src]!=INT_MAX && dist[dest]>dist[src]+weight)
+			{
+				dist[dest] = dist[src]+weight;
+			}
+		}
+	}
+
+	//The algorithm works fine with negative edges but does not work with negative weight cycles
+	//thus checking for any negative weight cycles...
+
+	for(int i=0;i<n;i++)
+	{
+			int src = get<0>(graph[i]);
+			int dest = get<1>(graph[i]);
+			int weight = get<2>(graph[i]);
+
+			if(dist[src]!=INT_MAX && dist[dest]>dist[src]+weight)
+			{
+				cout<<"Negative weight cycle detected..\n";
+				return false;
+			}
+	}
+
+	return true;
+
+}
+
+
+int main()
+{
+	//no. of vertices(V) & source(s)
+	int V = 6, s=0;
+
+	//graph containing all the weighted edges..
+	vector<tuple<int,int,int>>graph;
+
+	//inserting an edge with :
+	//src = 0
+	//dest = 1
+	// weight = 10
+	graph.push_back(make_tuple(0,1,10));
+	graph.push_back(make_tuple(0,2,8));
+	graph.push_back(make_tuple(1,4,2));
+	graph.push_back(make_tuple(2,3,1));
+	graph.push_back(make_tuple(3,1,-4));
+	graph.push_back(make_tuple(3,4,-1));
+	graph.push_back(make_tuple(4,5,-2));
+	graph.push_back(make_tuple(5,1,1));
+
+	//vector to store distances of all vertices from source(s)
+	vector<int>dist;
+	bool neg = bellman_ford(graph,V,s,dist);
+
+	//if no negative weigth cycle is found...
+	if(neg)
+	{
+		cout<<"vertex		Dist from Source\n";
+		for(int i=0;i<dist.size();i++)
+		{
+			cout<<i<<"\t\t\t"<<dist[i]<<"\n";
+		}
+	}
+
+
+	return 0;
+}