traversal.hpp

/*********************************************************************
 *
 * Linear Arrangement Library - A library that implements a collection
 * algorithms for linear arrangments of graphs.
 *
 * Copyright (C) 2019 - 2023
 *
 * This file is part of Linear Arrangement Library. The full code is available
 * at:
 *      https://github.com/LAL-project/linear-arrangement-library.git
 *
 * Linear Arrangement Library is free software: you can redistribute it
 * and/or modify it under the terms of the GNU Affero General Public License
 * as published by the Free Software Foundation, either version 3 of the
 * License, or (at your option) any later version.
 *
 * Linear Arrangement Library is distributed in the hope that it will be
 * useful, but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
 * GNU Affero General Public License for more details.
 *
 * You should have received a copy of the GNU Affero General Public License
 * along with Linear Arrangement Library.  If not, see <http://www.gnu.org/licenses/>.
 *
 * Contact:
 *
 *     Lluís Alemany Puig (lalemany@cs.upc.edu)
 *         LARCA (Laboratory for Relational Algorithmics, Complexity and Learning)
 *         CQL (Complexity and Quantitative Linguistics Lab)
 *         Jordi Girona St 1-3, Campus Nord UPC, 08034 Barcelona.   CATALONIA, SPAIN
 *         Webpage: https://cqllab.upc.edu/people/lalemany/
 *
 *     Ramon Ferrer i Cancho (rferrericancho@cs.upc.edu)
 *         LARCA (Laboratory for Relational Algorithmics, Complexity and Learning)
 *         CQL (Complexity and Quantitative Linguistics Lab)
 *         Office S124, Omega building
 *         Jordi Girona St 1-3, Campus Nord UPC, 08034 Barcelona.   CATALONIA, SPAIN
 *         Webpage: https://cqllab.upc.edu/people/rferrericancho/
 *
 ********************************************************************/
 
#pragma once
 
// C++ includes
#include <functional>
 
// lal includes
#include <lal/basic_types.hpp>
#include <lal/graphs/directed_graph.hpp>
#include <lal/graphs/undirected_graph.hpp>
#include <lal/detail/data_array.hpp>
#include <lal/detail/linear_queue.hpp>
 
namespace lal {
namespace detail {
 
template <
    class graph_t,
    std::enable_if_t< std::is_base_of_v<graphs::graph, graph_t>, bool > = true
>
class BFS {
public:
    typedef std::function<void (const BFS<graph_t>&, node)> BFS_process_one;
    typedef std::function<void (const BFS<graph_t>&, node, node, bool)> BFS_process_two;
    typedef std::function<bool (const BFS<graph_t>&, node)> BFS_bool_one;
    typedef std::function<bool (const BFS<graph_t>&, node, node)> BFS_bool_two;
 
public:
 
    static constexpr bool is_graph_directed =
        std::is_base_of_v<graphs::directed_graph, graph_t>;
    // ! Note that this member attribute is public, and so it should not have
    //   a leading 'm_' like the other private/protected members.
 
public:
    BFS(const graph_t& g) noexcept :
        m_G(g),
        m_vis(m_G.get_num_nodes())
    {
        reset();
    }
    ~BFS() noexcept = default;
 
    void reset() noexcept {
        clear_visited();
        m_queue.init(m_G.get_num_nodes());
 
        set_use_rev_edges(false);
        set_process_visited_neighbours(false);
 
        set_terminate_default();
        set_process_current_default();
        set_process_neighbour_default();
        set_node_add_default();
    }
 
    void start_at(node source) noexcept {
        m_queue.push(source);
        m_vis[source] = 1;
        do_traversal();
    }
 
    void start_at(const std::vector<node>& sources) noexcept {
        for (const node& u : sources) {
            m_queue.push(u);
            m_vis[u] = 1;
        }
        do_traversal();
    }
 
    /* SETTERS */
 
    void set_use_rev_edges(bool use) noexcept { m_use_rev_edges = use; }
 
    void set_terminate_default() noexcept
    { m_term = [](const BFS<graph_t>&, const node) -> bool { return false; }; }
    void set_terminate(const BFS_bool_one& f) noexcept
    { m_term = f; }
 
    void set_process_current_default() noexcept
    { m_proc_cur = [](const BFS<graph_t>&, const node) -> void { }; }
    void set_process_current(const BFS_process_one& f) noexcept
    { m_proc_cur = f; }
 
    void set_process_neighbour_default() noexcept
    { m_proc_neigh = [](const BFS<graph_t>&, const node, const node, bool) -> void { }; }
    void set_process_neighbour(const BFS_process_two& f) noexcept
    { m_proc_neigh = f; }
 
    void set_node_add_default() noexcept
    { m_add_node = [](const BFS<graph_t>&, const node, const node) -> bool { return true; }; }
    void set_node_add(const BFS_bool_two& f) noexcept
    { m_add_node = f; }
 
    void set_process_visited_neighbours(bool v) noexcept
    { m_proc_vis_neighs = v; }
 
    void clear_visited() noexcept { m_vis.fill(0); }
 
    void clear_queue() noexcept {
        m_queue.reset();
    }
 
    void set_visited(node u, char vis) noexcept {
#if defined DEBUG
        assert(vis == 0 or vis == 1);
#endif
        m_vis[u] = vis;
    }
 
    /* GETTERS */
 
    bool node_was_visited(node u) const noexcept { return m_vis[u] == 1; }
 
    bool all_visited() const noexcept {
        return std::all_of(m_vis.begin(), m_vis.end(), [](auto x){return x == 1;});
    }
 
    const graph_t& get_graph() const noexcept { return m_G; }
 
    const data_array<char>& get_visited() const noexcept { return m_vis; }
 
protected:
    void deal_with_neighbour(node s, node t, bool ltr) noexcept {
        // Process the neighbour 't' of 's'.
        const bool t_vis = node_was_visited(t);
 
        if ((not t_vis) or (t_vis and m_proc_vis_neighs)) {
            m_proc_neigh(*this, s, t, ltr);
        }
 
        if ((not t_vis) and m_add_node(*this, s, t)) {
            m_queue.push(t);
            // set node as visited
            m_vis[t] = 1;
        }
    }
 
    void process_neighbours(node s) noexcept {
        if constexpr (not is_graph_directed) {
            // for undirected graphs
 
            for (const node& t : m_G.get_neighbours(s)) {
                // Edges are processed in the direction "s -> t".
                // This is also the 'natural' orientation of the edge,
                // so this explains the 'true'.
                deal_with_neighbour(s, t, true);
            }
        }
        else {
            // for directed graphs
 
            for (const node& t : m_G.get_out_neighbours(s)) {
                // Edges are processed in the direction "s -> t".
                // This is also the 'natural' orientation of the edge,
                // hence the 'true'.
                deal_with_neighbour(s, t, true);
            }
            // process in-neighbours whenever appropriate
            if (m_use_rev_edges) {
                for (const node& t : m_G.get_in_neighbours(s)) {
                    // Edges are processed in the direction "s -> t".
                    // However, the 'natural' orientation of the edge
                    // is "t -> s", hence the 'false'.
                    deal_with_neighbour(s, t, false);
                }
            }
        }
    }
 
    void do_traversal() noexcept {
        while (m_queue.size() > 0) {
            const node s = m_queue.pop();
 
            // process current node
            m_proc_cur(*this, s);
 
            // check user-defined early termination condition
            if (m_term(*this, s)) { break; }
 
            process_neighbours(s);
        }
    }
 
protected:
    const graph_t& m_G;
 
    linear_queue<node> m_queue;
 
    data_array<char> m_vis;
    bool m_proc_vis_neighs = false;
    bool m_use_rev_edges = false;
 
protected:
    BFS_bool_one m_term;
 
    BFS_process_one m_proc_cur;
 
    BFS_process_two m_proc_neigh;
 
    BFS_bool_two m_add_node;
};
 
} // -- namespace detail
} // -- namespace lal