LintCode Topological Sorting

/**
* Definition for Directed graph.
* struct DirectedGraphNode {
*     int label;
*     vector<DirectedGraphNode *> neighbors;
*     DirectedGraphNode(int x) : label(x) {};
* };
*/
class Solution {
private:
unordered_set<DirectedGraphNode*> visited;

public:
/**
* @param graph: A list of Directed graph node
* @return: Any topological order for the given graph.
*/
vector<DirectedGraphNode*> topSort(vector<DirectedGraphNode*> graph) {
// write your code here
visited.clear();

vector<DirectedGraphNode*> path;

for (auto node : graph) {
dfs(node, path);
}
reverse(path.begin(), path.end());

return path;
}

void dfs(DirectedGraphNode* node, vector<DirectedGraphNode*>& path) {
if (visited.count(node) > 0) {
return;
}
visited.insert(node);

for (auto n : node->neighbors) {
dfs(n, path);
}

path.push_back(node);
}
};