Anderson.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
 
// lal includes
#include <lal/graphs/rooted_tree.hpp>
#include <lal/linarr/chunking/chunk.hpp>
#include <lal/detail/linarr/chunking/generic.hpp>
 
namespace lal {
namespace detail {
 
template <class arrangement_t>
class chunks_Anderson : public chunks_generic<arrangement_t> {
public:
    chunks_Anderson(const graphs::rooted_tree& rt, const arrangement_t& arr)
    noexcept
        : generic(rt, arr)
    {
    }
 
    void chunk_input_tree() noexcept {
        m_sequence.init(m_n);
 
        if (m_rt.get_num_nodes() == 1) {
            m_sequence.set_chunk_index(0, 0);
            m_sequence.push_chunk(0);
            last_chunk().set_root_node(0);
        }
        else {
            // assign chunk indices
            std::size_t chunk_idx = 0;
            assign_chunk_indices(m_rt.get_root(), chunk_idx);
 
            // relabel chunk indices from 0 to k so that chunk 0 is the
            // leftmost in the linear arrangement, and k is the rightmost
            relabel_chunks();
 
            // make chunks out of the map
            make_chunks();
        }
    }
 
private:
 
    [[nodiscard]] bool can_be_added(const node r, const node u) const noexcept {
        return m_rt.get_out_degree(u) == 0 and m_rt.has_edge(r, u);
    }
 
    void assign_chunk_indices(const node_t r, std::size_t& chunk_idx) noexcept {
        ++chunk_idx;
 
#if defined DEBUG
        assert(m_rt.get_out_degree(*r) > 0);
#endif
 
        set_chunk_index(*r, chunk_idx);
 
        // march leftwards in the arrangement assigning to the root's children
        // the same chunk index as the root
        position_t p_root = m_arr[r];
        if (p_root > 0ull) {
            position_t pl = p_root - 1ull;
            while (pl > 0ull and can_be_added(*r, m_arr[pl])) {
                set_chunk_index(m_arr[pl], chunk_idx);
                --pl;
            }
            // pl == 0
            if (can_be_added(*r, m_arr[pl])) {
                set_chunk_index(m_arr[pl], chunk_idx);
            }
        }
        // march rightwards in the arrangement assigning to the root's children
        // the same chunk index as the root
        if (p_root < m_n - 1) {
            position_t pr = p_root + 1ull;
            while (pr < m_n and can_be_added(*r, m_arr[pr])) {
                set_chunk_index(m_arr[pr], chunk_idx);
                ++pr;
            }
        }
 
        // assign new chunk indices to the terminal, unassigned children of 'r'
        for (node v : m_rt.get_out_neighbors(*r)) {
            if (node_to_chunk(v) > m_n and m_rt.get_out_degree(v) == 0) {
                set_chunk_index(v, chunk_idx);
                ++chunk_idx;
            }
        }
 
        // traverse down the tree and recursively build new chunks
        for (node_t v : m_rt.get_out_neighbors(*r)) {
            if (m_rt.get_out_degree(*v) > 0) {
                assign_chunk_indices(v, chunk_idx);
            }
        }
    }
 
    void relabel_chunks() noexcept {
        std::size_t chunk_idx = 0;
        position_t p = 0ull;
 
        while (p < m_n) {
            const std::size_t current_index = node_to_chunk(m_arr[p]);
 
            set_chunk_index(m_arr[p], chunk_idx);
            ++p;
 
            while (p < m_n and current_index == node_to_chunk(m_arr[p])) {
                set_chunk_index(m_arr[p], chunk_idx);
                ++p;
            }
 
            ++chunk_idx;
        }
    }
 
    void make_chunks() noexcept {
        m_sequence.push_chunk();
 
        position_t p = 0ull;
        while (p < m_n) {
 
            const std::size_t current_index = node_to_chunk(m_arr[p]);
 
            linarr::chunk& c = last_chunk();
            c.add_node(m_arr[p]);
 
            ++p;
            while (p < m_n and current_index == node_to_chunk(m_arr[p])) {
                c.add_node(m_arr[p]);
                ++p;
            }
 
            set_parent_chunk(c);
 
            if (p < m_n) {
                m_sequence.push_chunk();
            }
        }
    }
 
private:
 
    typedef chunks_generic<arrangement_t> generic;
 
    // member variables
    using generic::m_sequence;
    using generic::m_n;
    using generic::m_arr;
    using generic::m_rt;
 
    // member functions
    using generic::set_parent_chunk;
    using generic::set_chunk_index;
    using generic::node_to_chunk;
    using generic::last_chunk;
};
 
} // -- namespace detail
} // -- namespace lal