lintcode:Topological Sorting

For graph as follow:

顺便贴一个topology的视频：https://www.youtube.com/watch?v=ddTC4Zovtbc

/**
 * Definition for Directed graph.
 * struct DirectedGraphNode {
 *     int label;
 *     vector neighbors;
 *     DirectedGraphNode(int x) : label(x) {};
 * };
 */
class Solution {
    
private:
    void topSortHelper(DirectedGraphNode* curNode, stack &auxStack, set &visited)
    {
        visited.insert(curNode->label);
        
        for (int i=0; ineighbors.size(); i++)
        {
            if (visited.find(curNode->neighbors[i]->label) == visited.end()) 
            {
                topSortHelper(curNode->neighbors[i], auxStack, visited);
            }
        }
        auxStack.push(curNode);//当这个节点已经visit 过它所有的子节点的之后，就把它发到stack中，所以stack的最上层肯定是依赖性最小的，食物链最高的节点
    }
    
    
public:
    /**
     * @param graph: A list of Directed graph node
     * @return: Any topological order for the given graph.
     */
    vector topSort(vector graph) {
        // write your code here
        
        set visited;
        stack auxStack;
        
        for (int i=0; ilabel) == visited.end())
            {
                topSortHelper(graph[i], auxStack, visited);
            }
        }
        
        vector retVtr;
        while (auxStack.size() > 0)
        {
            retVtr.push_back(auxStack.top());
            auxStack.pop();
        }
        
        return retVtr;
    }
};