判断有向图是否存在回路—拓扑排序

#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)//创建有向图
{
	int i,j,k;
	string s1,s2;
	cout<<"请输入顶点数和边数:";
	cin>>g.num_vertex>>g.num_edge;
	cout<<"请输入顶点:";
	for(i=0;i<g.num_vertex;i++)
	{
		cin>>g.vertex_node[i].data;
		g.vertex_node[i].firstedge = NULL;
	}
	cout<<"请输入边:"<<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)//打印邻接表
{
	cout<<"邻接表如下:"<<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[])//计算每个顶点的入度
{
	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)//拓扑排序
{
	int indegree[10];//入度
	int count = 0;//计数

	find_indegree(g,indegree);

	int i;
	queue<int> q;
	for(i=0;i<g.num_vertex;i++)//把度为0的顶点入队
	{
		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)//将度为0的顶点的邻接顶点入度减1，如果变为0则将其入队
				q.push(p->adjvex);
			p=p->next;
		}
	}
	cout<<endl;
	if(count != g.num_vertex)//如果最终计数值和顶点数不相等，说明有的顶点入度没有变为0，存在环路
		cout<<"有向图存在环路!"<<endl;
}

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

测试用例一：

测试用例二：

参考：http://blog.youkuaiyun.com/cxllyg/article/details/7603157