Topological Sort

Hi this is a fast post, but I think it may be useful to a bunch of people.

Today I've experienced hard times in topological sort. I'm used to use a simple Depth-First-Search recursively to order the vertexes and store the order in the 'order' vector.

 void dfs(int x) {   
   vis[x] = true;   
   for(int u = 0; u < n; u++) {   
    if(!vis[u] && graph[x][u] == 1) {   
     dfs(u);   
    }   
   }   
   order.push_back(x);   
  }   

But, if the graph has a cycle ? in this way, the DFS will end normally and won't tell you that, a good strategy is to think to put colors in the nodes, Imagine like if a vertex is 'WHITE' it has not been visited yet, if a vertex is 'GREY' it has been visited, but it sub-trees hasn't been visited yet and 'BLACK' if the vertex has been visited and all it's sub-trees has been visited too. Taking it inside the code is easy, instead of use a 'boolean' array to check if the node is visited or not, use a numerical array 'int' and set values for the colors, in this example I'm using '0' for 'WHITE, '1' for 'GREY' and '2' for black, then here goes the right code. I have to thank AlexDmitriev, dalex and Malinovsky239 who answered me in the Codeforces forum and gave me this strategy. Thank you guys.

 void dfs(int x) {  
   vis[x] = 1;  
   for(int u = 0; u < n; u++) {  
     if(vis[u] == 1 && graph[x][u] == 1) has = true;  
     if(vis[u] == 0 && graph[x][u] == 1) {  
       dfs(u);  
     }  
   }  
   vis[x] = 2;  
   order.push_back(x);  
 }