map operation

__global__ void
bfs( const Edge * edges,
	Vertex * vertices,
	int current_depth )
{
	int e = blockDim.x * blockIdx.x + threadIdx.x;
	int vfirst = edges[e].first;
	int dfirst = vertices[vfirst];
	int vsecond = edges[e].second;
	int dsecond = vertices[vsecond];
	if ((dfirst == curent_depth) && (dsecond == -1)){
		vertices[vsecond] = dfirst + 1;
	}
	if (
		)
}