Dmin_Projective_HS.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/
 *
 *     Juan Luis Esteban (esteban@cs.upc.edu)
 *         LOGPROG: Logics and Programming Research Group
 *         Office 110, Omega building
 *         Jordi Girona St 1-3, Campus Nord UPC, 08034 Barcelona.   CATALONIA, SPAIN
 *         Webpage: https://www.cs.upc.edu/~esteban/
 *
 *     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/
 *
 ********************************************************************/
 
// C++ includes
#if defined DEBUG
#include <cassert>
#endif
#include <vector>
 
// lal includes
#include <lal/graphs/rooted_tree.hpp>
#include <lal/detail/linarr/Dmin_utils.hpp>
#include <lal/detail/linarr/Dopt_utils.hpp>
 
namespace lal {
namespace detail {
namespace Dmin {
namespace projective {
 
template <bool make_arrangement>
std::conditional_t<
    make_arrangement,
    std::pair<uint64_t, linear_arrangement>,
    uint64_t
>
HS(const graphs::rooted_tree& t) noexcept
{
#if defined DEBUG
    assert(t.is_rooted_tree());
#endif
 
    const uint64_t n = t.get_num_nodes();
    const node r = t.get_root();
    if (n == 1) {
        if constexpr (make_arrangement) {
            return {0, linear_arrangement::identity(1)};
        }
        else {
            return 0;
        }
    }
 
    // Make the sorted adjacency list rooted at the centroid of the tree.
    // This adjacency list is sorted non-increasingly by size of the subtrees.
    // LARGEST to SMALLEST
 
    std::vector<std::vector<node_size>> L(n);
    Dopt_utils::make_sorted_adjacency_list_rooted
        <sorting::non_increasing_t>
        (t, L);
 
    // construct the optimal projective arrangement
 
    if constexpr (make_arrangement) {
        linear_arrangement arr(n);
        const uint64_t D = Dmin_utils::embed<true>(L, r, arr);
        return {D, std::move(arr)};
    }
    else {
        linear_arrangement arr;
        const uint64_t D = Dmin_utils::embed<false>(L, r, arr);
        return D;
    }
}
 
} // -- namespace projective
} // -- namespace Dmin
} // -- namespace detail
} // -- namespace lal