added program for donut

Donut Turbo C++/Print_Topological_order.cpp

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+void printTopologicalOrder()
+{
+    //Assuming nodes in 0-indexing 0->n-1
+    //n=no. of nodes, adj-> adjacency list representation of graph
+    vector<int>inDegree(n,0);
+    //updating in degree for each node:
+    for(auto x:adj) for(auto y:x) inDegree[y]++;
+    queue<int>q;
+    for(int i=0;i<n;i++) if(inDegree[i]==0) q.push(i);
+    vector<int>topo; //to store the topological order
+    int s=0; //to store count of visited nodes
+    while(!q.empty())
+    {
+        int x=q.front();
+        q.pop();
+        topo.push_back(x);
+        for(auto it:a[x])
+            if(--inDegree[it]==0) q.push(it);
+        s++; // incrementing visited nodes
+    }
+    if(s==n) //print topo
+    else cout<<"The Graph is cyclic";
+}

Donut Turbo C++/README.txt

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+This program is to run a Donut program on turbo c++