Bellman_Ford_implementation.cpp

Bellman Ford algorithm implemented in C++

Author: Aman2632

classical_algorithms/c++/Bellman_Ford_Algo_Q.cpp

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+// BELLMAN FORD ALGORITHM TO DETECT NEGATIVE CYCLE IN GRAPHS....
+
+
+
+
+
+#include <bits/stdc++.h>
+using namespace std;
+
+typedef long long int ll;
+using ii= pair<ll,ll>;
+#define F first
+#define S second
+#define MP make_pair
+#define PB push_back
+
+
+struct Edge{                                    // we implement it using struct edge where each edge stores the edge details..
+    ll a,b,c;                                   //a->node,b->node,c->cost            (c)
+                                                                             //a--------->b  
+};
+
+
+vector<Edge> v;                                 // instead of creating a vector of piars , create a vector of edges where each element of the
+                                                // vector is an edge....
+void Bellman_Ford(ll n,ll m)                    // n-> nodes_no, m-> no_of_edges..
+{
+    vector<ll> d(n,1e18);      //holding min distance of nodes....
+    d[0]= 0;                   // initializing src at 0 distance
+    
+    ll x;                      // x-> flag for negative cycle....
+    
+    for(ll i=0;i;i++)        // after i iterations, i nodes will have attained there min distance provided -ve cycles not involved...
+    {<n
+        x=-1;
+        
+        for(ll j=0;j<m;j++)    // loop on all edges 
+        {
+            if(d[v[j].b]>d[v[j].a]+v[j].c)     // relax distance if u get any min_path
+            {
+                d[v[j].b]=d[v[j].a]+v[j].c;
+                x= v[j].a;                    
+            }
+        }
+    }
+    
+    
+    if(x!=-1)
+    {
+        cout<<"possible\n";     // got a negative cycle....
+    }
+    
+    else{
+        cout<<"not possible\n";    // otherwise not....
+    }
+    
+    
+}
+
+int main()
+{
+	ios_base::sync_with_stdio(false);
+	cin.tie(NULL);cout.tie(NULL);
+	
+	ll t;
+	cin>>t;
+	while(t--)
+	{
+	    ll n,m;
+	    cin>>n>>m;
+	    
+	    v.resize(m+1);                  // very important ...u may get RE if u dont resize v
+	    v.clear();                      // u must clear v if there are more than 1 test cases....
+	    
+	    
+	    for(ll i=0;i<m;i++)
+	    {
+	        ll x,y,z;
+	        cin>>x>>y>>z;
+	        
+	        v.PB({x,y,z});        
+	    }
+	    
+	    
+	    Bellman_Ford(n,m);
+	    
+	    
+	}
+}
+
+
+
+
+