Topological sort

Topological sort

Program to print in topological order and verify that given compilation order correctness based on the dependency of files :

// A C++ program to print topological sorting of a Directd Acyclic //Graph
#include <list>
#include <stack>
#include <algorithm>
using namespace std;
// Class to represent a graph
class Graph
    int V;    // No. of vertices’
    // Pointer to an array containing adjacency listsList
    list<int> *adj;
    // A function used by topologicalSort
    void topologicalSortUtil(int v, bool visited[], stack<int> &Stack);
    Graph(int V);   // Constructor
     // function to add an edge to graph
    void addEdge(int v, int w);
    // prints a Topological Sort of the complete graph
    void topologicalSort();
    bool edgeExist(int s, int d);
    bool isFollowingOrderAllowed( int *arr, int size);
Graph::Graph(int V)
    this->V = V;
    adj = new list<int>[V];
void Graph::addEdge(int v, int w)
    adj[v].push_back(w); // Add w to v’s list.
// A recursive function used by topologicalSort
void Graph::topologicalSortUtil(int v, bool visited[],
                                stack<int> &Stack)
    // Mark the current node as visited.
    visited[v] = true;
    // Recur for all the vertices adjacent to this vertex
    list<int>::iterator i;
    for (i = adj[v].begin(); i != adj[v].end(); ++i)
        if (!visited[*i])
            topologicalSortUtil(*i, visited, Stack);
    // Push current vertex to stack which stores result
// The function to do Topological Sort. It uses recursive
// topologicalSortUtil()
void Graph::topologicalSort()
    stack<int> Stack;
    // Mark all the vertices as not visited
    bool *visited = new bool[V];
    for (int i = 0; i < V; i++)
        visited[i] = false;
    // Call the recursive helper function to store Topological
    // Sort starting from all vertices one by one
    for (int i = 0; i < V; i++)
      if (visited[i] == false)
        topologicalSortUtil(i, visited, Stack);
    // Print contents of stack
    while (Stack.empty() == false)
        cout << << ” “;
bool Graph::edgeExist(int s, int d)
std::list<int>::iterator result = adj[s].begin();
result = std::find( result, adj[s].end(),d );
    if (result == adj[s].end()) return 0;
    return 1;
bool Graph::isFollowingOrderAllowed( int *arr, int size)
list<int>::iterator i;
    for (i = adj[4].begin(); i != adj[4].end(); ++i)
    cout << *i << “\t” ;
    for(int i = 0 ; i < size-1 ; i++)
if(! edgeExist(arr[i] , arr[i+1]))
return 0 ;
return 1 ;
// Driver program to test above functions
int main()
    // Create a graph given in the above diagram
    Graph g(6);
    g.addEdge(5, 2);
    g.addEdge(5, 0);
    g.addEdge(4, 0);
    g.addEdge(4, 1);
    g.addEdge(2, 3);
    g.addEdge(3, 1);
    cout << “Following is a Topological Sort of the given graph \n”;
    int arr[5] = {5,2,3};
    cout << endl << g.isFollowingOrderAllowed(arr,3) << endl;
    return 0;

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