图的拓扑序列（BFS)

way：找入度为0的节点删除，减少其他节点的入度，继续找入度为0的节点，直到删除完所有的图节点。（遍历node的neighbors就能得到neighbors的入度信息）

#include<iostream>
#include<vector>
#include<map>
#include<queue>
using namespace std;


class Node {
public:
	int label;
	vector<Node*> neighbors;
	Node(int x)
	{
		label=x;
	}
};


vector<Node*> topSort(vector<Node*> graph)
{
	map<Node*, int>indegreeMap;
	//统计所有节点的入度信息到indegreeMap中
	for(auto node: graph)
	{
		indegreeMap[node]=0;
	}

	for(auto node: graph)
	{
		for(auto next: node->neighbors)
		{
			indegreeMap[next] = indegreeMap[next]+1;
		}
	}

	//将入度为0的节点放入zeroQue中
	queue<Node*> zeroQue;
	for(auto pa: indegreeMap)
	{
		if(pa.second == 0)
		{
			zeroQue.push(pa.first);
		}
	}

	vector<Node*> result;

	//开始删除节点，减少入度
	while(!zeroQue.empty())
	{
		Node *cur = zeroQue.front();
		zeroQue.pop();
		result.push_back(cur);
		for(auto next: cur->neighbors)
		{
			indegreeMap[next] = indegreeMap[next]-1;
			if(indegreeMap[next]==0)
			{
				zeroQue.push(next);
			}
		}
	}
	return result;
}