E_iterator.hpp

/*********************************************************************
 *
 *  Linear Arrangement Library - A library that implements a collection
 *  algorithms for linear arrangments of graphs.
 *
 *  Copyright (C) 2019 - 2021
 *
 *  This file is part of Linear Arrangement Library. To see the full code
 *  visit the webpage:
 *      https://github.com/lluisalemanypuig/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 <utility>
#include <tuple>
 
// lal includes
#include <lal/graphs/directed_graph.hpp>
#include <lal/graphs/undirected_graph.hpp>
 
namespace lal {
namespace iterators {
 
template<
    typename GRAPH,
    bool is_directed = std::is_base_of_v<graphs::directed_graph, GRAPH>,
    std::enable_if_t<
        std::is_base_of_v<graphs::directed_graph, GRAPH> ||
        std::is_base_of_v<graphs::undirected_graph, GRAPH>
        , bool
    > = true
>
class E_iterator {
public:
    /* CONSTRUCTORS */
 
    E_iterator(const GRAPH& g) noexcept : m_G(g) {
        reset();
    }
    ~E_iterator() = default;
 
    /* GETTERS */
 
    inline bool end() const noexcept { return m_reached_end; }
 
    inline edge get_edge() const noexcept { return m_cur_edge; }
 
    /* MODIFIERS */
 
    inline void next() noexcept {
        if (not m_exists_next) {
            m_reached_end = true;
            return;
        }
 
        m_cur_edge = make_current_edge();
 
        // find the next edge
        std::tie(m_exists_next, m_cur) = find_next_edge();
    }
 
    inline void reset() noexcept {
        __reset();
        next();
    }
 
private:
    typedef std::pair<node,std::size_t> E_pointer;
 
private:
    const GRAPH& m_G;
    E_pointer m_cur;
    bool m_exists_next = true;
    bool m_reached_end = false;
    edge m_cur_edge;
 
private:
    inline void __reset() noexcept {
        m_exists_next = true;
        m_reached_end = false;
 
        m_cur.first = 0;
        m_cur.second = static_cast<std::size_t>(-1);
 
        auto [found, new_pointer] = find_next_edge();
        if (not found) {
            // if we can't find the next edge, then there is no next...
            m_exists_next = false;
            m_reached_end = true;
            return;
        }
 
        // since an edge was found, store it in current
        m_cur = new_pointer;
        m_cur_edge = make_current_edge();
 
        // how do we know there is a next edge?
        // well, find it!
        auto [f2, _] = find_next_edge();
        m_exists_next = f2;
 
#if defined DEBUG
        if (m_G.get_num_edges() == 1) {
            assert(m_exists_next == false);
            assert(m_reached_end == false);
        }
#endif
 
        // this is the case of the graph having only one edge
        if (not m_exists_next) {
            m_exists_next = true;
        }
    }
 
    inline edge make_current_edge() const noexcept {
        node s, t;
        if constexpr (is_directed) {
            s = m_cur.first;
            t = m_G.get_out_neighbours(s)[m_cur.second];
        }
        else {
            s = m_cur.first;
            t = m_G.get_neighbours(s)[m_cur.second];
        }
        return edge(s,t);
    }
 
    template<bool isdir = is_directed, std::enable_if_t<isdir, bool> = true>
    inline std::pair<bool, E_pointer> find_next_edge() const noexcept {
        const uint32_t n = m_G.get_num_nodes();
 
        node s = m_cur.first;
        std::size_t pt = m_cur.second;
        bool found = false;
 
        ++pt;
        if (s < n and pt < m_G.get_out_degree(s)) {
            found = true;
        }
        else {
            pt = 0;
            ++s;
            while (s < n and m_G.get_out_degree(s) == 0) { ++s; }
            found = s < n;
        }
        return make_pair(found, E_pointer(s, pt));
    }
    template<bool isdir = is_directed, std::enable_if_t<not isdir, bool> = true>
    inline std::pair<bool, E_pointer> find_next_edge() const noexcept {
        const uint32_t n = m_G.get_num_nodes();
 
        node s = m_cur.first;
        std::size_t pt = m_cur.second + 1;
        bool found = false;
 
        while (s < n and not found) {
            const auto& Ns = m_G.get_neighbours(s);
            while (pt < Ns.size() and s > Ns[pt]) { ++pt; }
 
            found = pt < Ns.size();
            if (not found) {
                ++s;
                pt = 0;
            }
        }
        return make_pair(found, E_pointer(s, pt));
    }
};
 
} // -- namespace iterators
} // -- namespace lal