查找有向图中的环

根据“算法导论”中的DFS算法实现。

如下：

#include 
enum
{
	WHITE,
	GRAY,
	BLACK
};

struct vertex
{
	int color;
	int d, f;
	int parent;
};

int time = 0;
void dfs_visit(int matrix[][6], struct vertex *v, int index);

void dfs(int matrix[][6], struct vertex *v)
{
	int i;
	for(i = 0; i < 6; i++)
	{
		v[i].color = WHITE;
		v[i].d = 0;
		v[i].f = 0;
		v[i].parent = -1;
	}

	for(i = 0; i < 6; i++)
	{
		if(v[i].color == WHITE)
		{
			dfs_visit(matrix, v, i);
//			printf("\n");
		}
	}
}

int tmp[6];
int g_index = 0;
void dfs_visit(int matrix[][6], struct vertex *v, int index)
{
//	printf(" %d", index);
	if(v[index].color == WHITE)
	{
		tmp[g_index] = index;
		g_index++;
	}

	time += 1;
	v[index].d = time;
	v[index].color = GRAY;
	
	int i;
	for(i = 0; i < 6; i++)
	{
		if(matrix[index][i] && v[i].color == WHITE)
		{
			v[i].parent = index;
			dfs_visit(matrix, v, i);
		}
		else if(v[i].color == GRAY && matrix[index][i])
		{
			int j = 0;
			while(tmp[j] != i)
			{
				j++;
			}

			while( j < g_index)
			{
				printf("%d -->", tmp[j]);
				j++;
			}
			printf("%d\n", i);
		}
	}
	
	time += 1;
	v[index].f = time;
	v[index].color =BLACK;
	g_index--;
}

int main(int argc, char **argv)
{
	int matrix[6][6] = 
	{
		{1, 1, 0, 1, 1, 0},
		{0, 0, 1, 0, 0, 0},
		{1, 0, 0, 0, 0, 0},
		{0, 0, 0, 0, 1, 0},
		{0, 0, 0, 0, 0, 1},
		{0, 0, 0, 1, 0, 0}
	};

	struct vertex v[6];

	dfs(matrix, v);
	return 0;	
}

输出：

0 -->0
0 -->1 -->2 -->0
3 -->4 -->5 -->3