数据结构---拓扑排序

给出一个图的结构，输出其拓扑排序序列，要求在同等条件下，编号小的顶点在前 

 输入

        若干行整数，第一行有2个数，分别为顶点数v和弧数a，接下来有a行，每一行有2个数，分别是该条弧所关联的两个顶点编号

输出

        若干个空格隔开的顶点构成的序列(用小写字母)

#include<iostream>
#include<cstdio>
#include<algorithm>
using namespace std;
const int MaxSize = 20;
struct edge_Node
{
	int data;
	edge_Node* next;
};
struct head_Node
{
	int indegree;
	int data;
	edge_Node* first;
};
class Graph
{
public:
	Graph(string Vertex[],int vNum,int eNum)
	{
		edge_Node* s;
		this->vertexNum = vNum;
		this->edgeNum = eNum;
		for (int i = 0; i < this->vertexNum; i++)
		{
			vertex[i] = Vertex[i];
			headList[i].data = i;
			headList[i].first = NULL;
			headList[i].indegree = 0;
		}
		for (int j = 0; j < this->edgeNum; j++)
		{
			int front, rear;
			cin >> front >> rear;
			front = front - 1;
			rear = rear - 1;
			headList[rear].indegree++;
			s = new edge_Node;
			s->data = rear;
			s->next = headList[front].first;//头插法
			headList[front].first = s;
		}
	}
	void top_Sort()
	{
		int rear = -1;
		int Q[MaxSize];
		int p;
		edge_Node* ptr = NULL;
		for (int i = 0; i < vertexNum; i++)
		{
			if (headList[i].indegree == 0)
			{
				Q[++rear] = i;
			}
		}
		sort(Q, Q + (rear + 1),greater<int>());
		while (rear != -1)
		{
			p = Q[rear--];
			cout << vertex[headList[p].data]<<" ";
			ptr = headList[p].first;
			while (ptr != NULL)
			{
				headList[ptr->data].indegree--;
				if (headList[ptr->data].indegree == 0)
				{
					Q[++rear] = ptr->data;
				}
				ptr = ptr->next;
 			}
			sort(Q, Q + (rear + 1), greater<int>());
		}
	}
private:
	int vertexNum;
	int edgeNum;
	string vertex[MaxSize];
	head_Node headList[MaxSize];
};
 
int main()
{
	string data[] = { "v1","v2","v3","v4","v5","v6","v7","v8"};
	int vNum, eNum;
	cin >> vNum >> eNum;//输入顶点和边的个数
	Graph graph(data, vNum, eNum);
	graph.top_Sort();
	return 0;
}