#include<iostream> #include<list> #include<stack> using namespace std; class Graph {  int vertexNum;  list<int> *adjacents; public:  Graph(int _vertexNum) {   vertexNum = _vertexNum;   adjacents = new list<int>[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<int>::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<int> 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 << v << " ";   ver_count++;   for (list<int>::iterator iter = adjacents[v].begin(); iter != adjacents[v].end(); iter++) {    if (0 == --indegree[*iter])     m_stack.push(*iter);   }  }  cout << endl;  if (ver_count < vertexNum)   return false;  return true; } int main(int argc, char *argv[]) {  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);  if (g.topologicalSort())   cout << "it is a topological graph" << endl;  else   cout << "it is not a topological graph" << endl;  cin.get();  return 0; }