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24.BellmanFord.cpp

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+/*
+ *  This program constructs a graph from user inputs and
+ *  find a single source shortest path using
+ *  Ballman-Ford algorithm
+ *
+ *      Coded by: Abdurrezak Efe
+ *
+ * */
+
+#include <iostream>
+#include <vector>
+using namespace std;
+typedef pair< int , int> edge;
+
+//constructing the graph
+class Graph{
+
+public:
+
+    vector <pair<int , edge >> edges;
+    int v;
+    int e;
+
+    Graph(int v, int e)
+    {
+        //edges.resize(e);
+        this->v = v;
+        this->e = e;
+    }
+
+    void add_edge(int x, int y, int w)
+    {
+        edge ee = {x,y};
+        pair<int, edge> newedge= {w, ee};
+        edges.push_back(newedge);
+    }
+
+};
+
+
+bool bellman_ford(Graph g)
+{
+    //initializing arrays
+    int distance[g.v];
+    int previous[g.v];
+
+    for(int i=0;i<g.v;i++)
+        distance[i] = 999999999, previous[i] = -1;
+
+    distance[0] = 0;
+
+    //updating the distance in every step
+    for(int i=0;i<g.v-1;i++)
+    {
+        for(int j=0;j<g.edges.size();j++)
+        {
+            int u,v,w;
+            u = g.edges[j].second.first;
+            v = g.edges[j].second.second;
+            w = g.edges[j].first;
+            if(distance[u] + w < distance[v] )
+                distance[v] = distance[u] + w, previous[v] = u;
+        }
+    }
+
+    //checking negative weight cycles
+    for(int j=0;j<g.edges.size();j++)
+    {
+        int u,v,w;
+        u = g.edges[j].second.first;
+        v = g.edges[j].second.second;
+        w = g.edges[j].first;
+        if(distance[u] + w < distance[v] )
+        {
+            cout << "Negative cycle detected! " << endl;
+            return false;
+        }
+    }
+
+
+    for(int i=0;i<g.v;i++)
+        cout << "vertex: "<< i << " distance: " << distance[i] << " parent: " << previous[i] << endl;
+
+
+    return 1;
+}
+
+
+int main()
+{
+    int v,e;
+    cin >> v >> e;
+
+    Graph g(v,e);
+
+    int x,y,w;
+    for(int i=0;i<e;i++)
+    {
+        cin >> x >> y >> w;
+        g.add_edge(x,y,w);
+    }
+
+    bellman_ford(g);
+}