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/*
* Copyright 2008-2009 NVIDIA Corporation
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
#include <deque>
#include <cusp/exception.h>
namespace cusp
{
namespace graph
{
namespace detail
{
namespace host
{
template<bool MARK_PREDECESSORS, typename MatrixType, typename ArrayType>
void breadth_first_search(const MatrixType& G, const typename MatrixType::index_type src, ArrayType& labels)
{
typedef typename MatrixType::index_type VertexId;
ArrayType predecessors;
// initialize predecessor array
if(MARK_PREDECESSORS) predecessors.resize(G.num_rows);
// initialize distances
for (size_t i = 0; i < G.num_rows; i++) {
labels[i] = -1;
}
labels[src] = 0;
VertexId search_depth = 0;
// Initialize queue for managing previously-discovered nodes
std::deque<VertexId> frontier;
frontier.push_back(src);
//
// Perform BFS
//
while (!frontier.empty()) {
// Dequeue node from frontier
VertexId dequeued_node = frontier.front();
frontier.pop_front();
VertexId neighbor_dist = labels[dequeued_node] + 1;
// Locate adjacency list
int edges_begin = G.row_offsets[dequeued_node];
int edges_end = G.row_offsets[dequeued_node + 1];
for (int edge = edges_begin; edge < edges_end; edge++) {
// Lookup neighbor and enqueue if undiscovered
VertexId neighbor = G.column_indices[edge];
if (neighbor == -1) continue;
if (labels[neighbor] == -1) {
labels[neighbor] = neighbor_dist;
if (search_depth < neighbor_dist) {
search_depth = neighbor_dist;
}
if(MARK_PREDECESSORS) predecessors[neighbor] = dequeued_node;
frontier.push_back(neighbor);
}
}
}
search_depth++;
// if predecessors are needed then copy into outgoing array
if(MARK_PREDECESSORS) labels = predecessors;
}
} // end namespace host
} // end namespace detail
} // end namespace graph
} // end namespace cusp
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