class Graph {
 int vertexNum;
 list *adjacents;
public:
 Graph(int _vertexNum) {
  vertexNum = _vertexNum;
  adjacents = new list[vertexNum];
 }
 void findIndegree(int *indegree, int n);
 bool topologicalSort();
 void addEdge(int v, int w);
};

void Graph::addEdge(int v, int w) {
 adjacents[v].push_back(w);
}

void Graph::findIndegree(int *indegree, int n) {
 int v;
 list::iterator iter;
 for(v = 0; v < vertexNum; v++) {
  for (iter = adjacents[v].begin(); iter != adjacents[v].end(); iter++)
   indegree[*iter]++;
 }
}

bool Graph::topologicalSort() {
 int ver_count = 0;
 stack m_stack;
 int *indegree = new int[vertexNum];
 memset(indegree, 0, sizeof(int) * vertexNum);
 findIndegree(indegree, vertexNum);
 int v;
 for (v = 0; v < vertexNum; v++)
  if (0 == indegree[v])
   m_stack.push(v);
 while (!m_stack.empty()) {
  v = m_stack.top();
  m_stack.pop();
  cout