lintcode-拓扑排序-127

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

vector<DirectedGraphNode*> topSort(vector<DirectedGraphNode*> graph) {
vector<DirectedGraphNode*> ret;
if(graph.empty())
return ret;

map<DirectedGraphNode*,int> in; //in为入度
stack<DirectedGraphNode*>   s;  //保存入度为零的节点
for(auto e:graph){
for(auto i:e->neighbors)
++in[i];              //记录每个节点的入度
}

for(auto e:graph)
if(0==in[e])
s.push(e);         //入度为零的节点入栈

while(!s.empty()){        //BFS遍历,搜寻入度为零的节点
DirectedGraphNode* cur=s.top();
s.pop();             //当前节点出栈时，它的相邻节点入度都减一
ret.push_back(cur);
for(auto e:cur->neighbors){
if(--in[e]==0)    //减一后为零则入栈
s.push(e);
}
}
return ret;
}
};