131 lines
3.7 KiB
C++
131 lines
3.7 KiB
C++
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// boost heap: heap merge algorithms
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//
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// Copyright (C) 2011 Tim Blechmann
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//
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// Distributed under the Boost Software License, Version 1.0. (See
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// accompanying file LICENSE_1_0.txt or copy at
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// http://www.boost.org/LICENSE_1_0.txt)
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#ifndef BOOST_HEAP_MERGE_HPP
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#define BOOST_HEAP_MERGE_HPP
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#include <boost/concept/assert.hpp>
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#include <boost/heap/heap_concepts.hpp>
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#include <boost/type_traits/is_same.hpp>
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#ifdef BOOST_HAS_PRAGMA_ONCE
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#pragma once
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#endif
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namespace boost {
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namespace heap {
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namespace detail {
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template <typename Heap1, typename Heap2>
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struct heap_merge_emulate
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{
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struct dummy_reserver
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{
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static void reserve (Heap1 & lhs, std::size_t required_size)
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{}
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};
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struct reserver
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{
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static void reserve (Heap1 & lhs, std::size_t required_size)
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{
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lhs.reserve(required_size);
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}
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};
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typedef typename boost::mpl::if_c<Heap1::has_reserve,
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reserver,
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dummy_reserver>::type space_reserver;
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static void merge(Heap1 & lhs, Heap2 & rhs)
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{
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if (Heap1::constant_time_size && Heap2::constant_time_size) {
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if (Heap1::has_reserve) {
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std::size_t required_size = lhs.size() + rhs.size();
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space_reserver::reserve(lhs, required_size);
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}
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}
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// FIXME: container adaptors could benefit from first appending all elements and then restoring the heap order
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// FIXME: optimize: if we have ordered iterators and we can efficiently insert keys with a below the lowest key in the heap
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// d-ary, b and fibonacci heaps fall into this category
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while (!rhs.empty()) {
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lhs.push(rhs.top());
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rhs.pop();
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}
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lhs.set_stability_count((std::max)(lhs.get_stability_count(),
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rhs.get_stability_count()));
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rhs.set_stability_count(0);
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}
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};
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template <typename Heap>
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struct heap_merge_same_mergable
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{
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static void merge(Heap & lhs, Heap & rhs)
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{
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lhs.merge(rhs);
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}
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};
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template <typename Heap>
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struct heap_merge_same
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{
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static const bool is_mergable = Heap::is_mergable;
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typedef typename boost::mpl::if_c<is_mergable,
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heap_merge_same_mergable<Heap>,
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heap_merge_emulate<Heap, Heap>
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>::type heap_merger;
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static void merge(Heap & lhs, Heap & rhs)
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{
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heap_merger::merge(lhs, rhs);
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}
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};
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} /* namespace detail */
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/** merge rhs into lhs
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*
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* \b Effect: lhs contains all elements that have been part of rhs, rhs is empty.
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*
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* */
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template <typename Heap1,
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typename Heap2
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>
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void heap_merge(Heap1 & lhs, Heap2 & rhs)
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{
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BOOST_CONCEPT_ASSERT((boost::heap::PriorityQueue<Heap1>));
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BOOST_CONCEPT_ASSERT((boost::heap::PriorityQueue<Heap2>));
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// if this assertion is triggered, the value_compare types are incompatible
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BOOST_STATIC_ASSERT((boost::is_same<typename Heap1::value_compare, typename Heap2::value_compare>::value));
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const bool same_heaps = boost::is_same<Heap1, Heap2>::value;
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typedef typename boost::mpl::if_c<same_heaps,
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detail::heap_merge_same<Heap1>,
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detail::heap_merge_emulate<Heap1, Heap2>
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>::type heap_merger;
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heap_merger::merge(lhs, rhs);
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}
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} /* namespace heap */
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} /* namespace boost */
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#endif /* BOOST_HEAP_MERGE_HPP */
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