E_iterator.hpp

/*********************************************************************
 *
 * Linear Arrangement Library - A library that implements a collection
 * algorithms for linear arrangments of graphs.
 *
 * Copyright (C) 2019 - 2024
 *
 * 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 (lluis.alemany.puig@upc.edu)
 *         LQMC (Quantitative, Mathematical, and Computational Linguisitcs)
 *         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)
 *         LQMC (Quantitative, Mathematical, and Computational Linguisitcs)
 *         CQL (Complexity and Quantitative Linguistics Lab)
 *         Office 220, 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_t,
    bool is_directed = std::is_base_of_v<graphs::directed_graph, graph_t>,
    std::enable_if_t<std::is_base_of_v<graphs::graph, graph_t>, bool> = true
>
class E_iterator {
public:
    /* CONSTRUCTORS */
 
    E_iterator(const graph_t& g) noexcept :
        m_G(g),
        m_num_nodes(m_G.get_num_nodes())
    {
        reset();
    }
    ~E_iterator() = default;
 
    /* GETTERS */
 
    [[nodiscard]] bool end() const noexcept { return m_reached_end; }
 
    [[nodiscard]] const edge& get_edge() const noexcept { return m_cur_edge; }
 
    [[nodiscard]] edge_t get_edge_t() const noexcept { return m_cur_edge; }
 
    [[nodiscard]] edge yield_edge() noexcept {
        const auto e = get_edge();
        next();
        return e;
    }
 
    [[nodiscard]] edge_t yield_edge_t() noexcept {
        const auto e = get_edge_t();
        next();
        return e;
    }
 
    /* MODIFIERS */
 
    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();
    }
 
    void reset() noexcept {
        __reset();
        next();
    }
 
private:
    typedef std::pair<node,std::size_t> E_pointer;
 
private:
    const graph_t& m_G;
    const uint64_t m_num_nodes;
 
    E_pointer m_cur;
    bool m_exists_next;
    bool m_reached_end;
    edge m_cur_edge;
 
private:
    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(not m_exists_next);
            assert(not m_reached_end);
        }
#endif
 
        // this is the case of the graph having only one edge
        if (not m_exists_next) {
            m_exists_next = true;
        }
    }
 
    [[nodiscard]] edge make_current_edge() const noexcept {
        node s, t;
        if constexpr (is_directed) {
            s = m_cur.first;
            t = m_G.get_out_neighbors(s)[m_cur.second];
        }
        else {
            s = m_cur.first;
            t = m_G.get_neighbors(s)[m_cur.second];
        }
        return {s,t};
    }
 
    template <bool isdir = is_directed, std::enable_if_t<isdir, bool> = true>
    [[nodiscard]] std::pair<bool, E_pointer> find_next_edge() const noexcept {
        node s = m_cur.first;
        std::size_t pt = m_cur.second;
        bool found = false;
 
        ++pt;
        if (s < m_num_nodes and pt < m_G.get_out_degree(s)) {
            found = true;
        }
        else {
            pt = 0;
            ++s;
            while (s < m_num_nodes and m_G.get_out_degree(s) == 0) { ++s; }
            found = s < m_num_nodes;
        }
        return {found, E_pointer(s, pt)};
    }
    template <bool isdir = is_directed, std::enable_if_t<not isdir, bool> = true>
    [[nodiscard]] std::pair<bool, E_pointer> find_next_edge() const noexcept {
        node s = m_cur.first;
        std::size_t pt = m_cur.second + 1;
        bool found = false;
 
        while (s < m_num_nodes and not found) {
            const auto& Ns = m_G.get_neighbors(s);
            while (pt < Ns.size() and s > Ns[pt]) { ++pt; }
 
            found = pt < Ns.size();
            if (not found) {
                ++s;
                pt = 0;
            }
        }
        return {found, E_pointer(s, pt)};
    }
};
 
} // -- namespace iterators
} // -- namespace lal