#include <iostream>
#include <string>
#include <queue>
using namespace std;

typedef struct Edgenode
{
	int adjvex;
	struct Edgenode *next;
}Edgenode;

typedef struct Vertexnode
{
	string data;
	Edgenode *firstedge;
}Vertexnode,Adjlist[10];

typedef struct Graph
{
	Adjlist vertex_node;
	int num_vertex;
	int num_edge;
}Graph;

int get_location(Graph g, string s)
{
	int i;
	for(i=0;i<g.num_vertex;i++)
	{
		if(s == g.vertex_node[i].data)
			return i;
	}
	return -1;
}

void create_graph(Graph &g)//建立有向圖
{
	int i,j,k;
	string s1,s2;
	cout<<"請輸入頂點數和邊數:";
	cin>>g.num_vertex>>g.num_edge;
	cout<<"請輸入頂點:";
	for(i=0;i<g.num_vertex;i++)
	{
		cin>>g.vertex_node[i].data;
		g.vertex_node[i].firstedge = NULL;
	}
	cout<<"請輸入邊:"<<endl;
	for(k=0;k<g.num_edge;k++)
	{
		cin>>s1>>s2;
		i = get_location(g,s1);
		j = get_location(g,s2);
		Edgenode *p = new Edgenode();
		p->adjvex = j;
		p->next = g.vertex_node[i].firstedge;
		g.vertex_node[i].firstedge = p;
	}
}

void print_graph(Graph g)//列印鄰接表
{
	cout<<"鄰接表如下:"<<endl;
	int i;
	for(i=0;i<g.num_vertex;i++)
	{
		cout<<g.vertex_node[i].data;
		Edgenode *p = g.vertex_node[i].firstedge;
		while(p)
		{
			cout<<"->"<<g.vertex_node[p->adjvex].data;
			p = p->next;
		}
		cout<<endl;
	}
}

void find_indegree(Graph g, int indegree[])//計算每個頂點的入度
{
	int i;
	for(i=0;i<g.num_vertex;i++)
		indegree[i]=0;
	for(i=0;i<g.num_vertex;i++)
	{
		Edgenode *p = g.vertex_node[i].firstedge;
		while(p)
		{
			indegree[p->adjvex]++;
			p=p->next;
		}
	}
}

void topologicalsort(Graph g)//拓撲排序
{
	int indegree[10];//入度
	int count = 0;//計數

	find_indegree(g,indegree);

	int i;
	queue<int> q;
	for(i=0;i<g.num_vertex;i++)//把度為0的頂點入隊
	{
		if(indegree[i]==0)
			q.push(i);
	}
	while(!q.empty())
	{
		int k = q.front();
		q.pop();
		cout<<g.vertex_node[k].data<<" ";
		count++;
		Edgenode *p = g.vertex_node[k].firstedge;
		while(p)
		{
			if(--indegree[p->adjvex]==0)//將度為0的頂點的鄰接頂點入度減1，如果變為0則將其入隊
				q.push(p->adjvex);
			p=p->next;
		}
	}
	cout<<endl;
	if(count != g.num_vertex)//如果最終計數值和頂點數不相等，說明有的頂點入度沒有變為0，存在環路
		cout<<"有向圖存在環路!"<<endl;
}

int main()
{
	Graph g;
	create_graph(g);
	print_graph(g);
	cout<<"拓撲排序:"<<endl;
	topologicalsort(g);
	return 0;
}
 

測試用例一：

測試用例二：

參考：http://blog.csdn.net/cxllyg/article/details/7603157