有向图算法之拓扑排序

/**
 * Definition for Directed graph.
 * struct DirectedGraphNode {
 *     int label;
 *     vector<DirectedGraphNode *> neighbors;
 *     DirectedGraphNode(int x) : label(x) {};
 * };
 */
 
//使用bfs进行拓扑排序：
//1、统计各个节点的入度信息，
//2、查找入度为0的点放入队列和返回的vector中初始化bfs的队列
//3、进行bfs，将从队列中弹出的元素的neighbors的入度减1然后判断该节点入度是否为0.为0
//   则加入队列同时加入返回vector中（这一步的主要框架就是bfs的程序框架）
class Solution {
public:

    vector<DirectedGraphNode*> topSort(vector<DirectedGraphNode*> graph) {
        // write your code here
        //1、得到所有节点的入度信息
        map<DirectedGraphNode*, int> indegree = getIndegree(graph);
        
        //2、将入度为0的放入队列
        
        return addQueue(indegree, graph);
        
    }
    
    map<DirectedGraphNode*, int> getIndegree(vector<DirectedGraphNode*> graph){
        int size = graph.size();
        map<DirectedGraphNode*, int> res;
        if(size == 0){
            return res;
        }
        
        for(int i = 0; i < size; i++){
            DirectedGraphNode* temp = graph[i];
             if(res.find(temp) == res.end()){
                    res[temp] = 0;
             }
            int nbSize = temp->neighbors.size();
            for(int i = 0; i < nbSize; i++){
                DirectedGraphNode* nbNode = temp->neighbors[i];
                if(res.find(nbNode) == res.end()){
                    res[nbNode] = 1;
                    continue;
                }
                res[nbNode]++;
            }
        }
        return res;
    }
    
    vector<DirectedGraphNode*> addQueue(map<DirectedGraphNode*, int>& indegree,vector<DirectedGraphNode*>& graph){
        vector<DirectedGraphNode*> res;
        if(graph.size() == 0){
            return res;
        }
        
        queue<DirectedGraphNode*> nodeQueue;
        //找到一个入度为0的点
        for(auto it = indegree.begin(); it != indegree.end(); ++it){
            if(it->second == 0){
                nodeQueue.push(it->first);
                res.push_back(it->first);
            }
        }
        
        while(nodeQueue.empty() != true){
            DirectedGraphNode* temp = nodeQueue.front();
            nodeQueue.pop();
            int nbSize = temp->neighbors.size();
            for(int i = 0; i < nbSize; i++){
                indegree[temp->neighbors[i]]--;
                if(indegree[temp->neighbors[i]] == 0){
                    nodeQueue.push(temp->neighbors[i]);
                    res.push_back(temp->neighbors[i]);
                }
            }
        }
        
        return res;
        
    }
};