branchless_path.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 <optional>
#if defined DEBUG
#include <cassert>
#endif
 
// lal includes
#include <lal/basic_types.hpp>
#include <lal/detail/array.hpp>
#include <lal/graphs/tree.hpp>
 
namespace lal {
namespace properties {
 
class branchless_path {
public:
 
    /* MODIFIERS */
 
    void init(std::size_t n) noexcept {
        m_lowest_lexicographic.reset();
        m_h1 = m_h2 = n + 1;
        m_vertex_sequence.clear();
        m_vertex_sequence.reserve(n);
        m_vertex_set.resize(n, 0);
        m_position.resize(n, n + 1);
    }
 
    void add_node(node u) noexcept {
        m_vertex_set[u] = 1;
        m_vertex_sequence.push_back(u);
        m_position[u] = m_vertex_sequence.size() - 1;
    }
 
    /* SETTERS */
 
    void set_h1(node h) noexcept { m_h1 = h; }
    void set_h2(node h) noexcept { m_h2 = h; }
    void set_lowest_lexicographic(node l) noexcept { m_lowest_lexicographic = l; }
 
    /* GETTERS */
 
    [[nodiscard]] node operator[](std::size_t i) const noexcept {
#if defined DEBUG
        assert(i < m_vertex_sequence.size());
#endif
        return m_vertex_sequence[i];
    }
 
    [[nodiscard]] node get_h1() const noexcept { return m_h1; }
    [[nodiscard]] node get_h2() const noexcept { return m_h2; }
 
    [[nodiscard]] bool has_lowest_lexicographic() const noexcept {
        return m_lowest_lexicographic.has_value();
    }
    [[nodiscard]] node get_lowest_lexicographic() const noexcept {
#if defined DEBUG
        assert(has_lowest_lexicographic());
#endif
        return *m_lowest_lexicographic;
    }
    [[nodiscard]] const std::vector<node>& get_vertex_sequence() const noexcept
    { return m_vertex_sequence; }
 
    [[nodiscard]] std::size_t get_num_nodes() const noexcept
    { return m_vertex_sequence.size(); }
    [[nodiscard]] std::size_t get_num_edges() const noexcept
    { return m_vertex_sequence.size() - 1; }
    [[nodiscard]] bool has_node(node u) const noexcept { return m_vertex_set[u] == 1; }
    [[nodiscard]] std::size_t get_position(node u) const noexcept {
#if defined DEBUG
        assert(has_node(u));
#endif
        return m_position[u];
    }
 
    template <class graph_t>
    [[nodiscard]] bool is_antenna(const graph_t& t) const noexcept {
        static_assert(std::is_base_of_v<graphs::graph, graph_t>);
        return t.get_degree(m_h1) == 1 or t.get_degree(m_h2) == 1;
    }
 
private:
    detail::array<char> m_vertex_set;
    detail::array<std::size_t> m_position;
    std::vector<node> m_vertex_sequence;
 
    node m_h1;
    node m_h2;
    std::optional<node> m_lowest_lexicographic;
};
 
} // -- namespace properties
} // -- namespace lal