96 lines
2.2 KiB
C++
96 lines
2.2 KiB
C++
// SPDX-License-Identifier: BSD-2-Clause
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// author: Max Kellermann <max.kellermann@gmail.com>
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#pragma once
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#include "StaticVector.hxx"
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#include <algorithm> // for std::find_if()
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#include <concepts>
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/**
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* Move all items from #src to #dest, keeping both sorted.
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*
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* @param p the predicate by which both lists are already
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* sorted
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*/
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template<typename List>
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constexpr void
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MergeList(List &dest, List &src,
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std::predicate<typename List::const_reference, typename List::const_reference> auto p) noexcept
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{
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const auto dest_end = dest.end(), src_end = src.end();
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auto dest_at = dest.begin();
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while (!src.empty()) {
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const auto src_begin = src.begin();
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/* find the first item of "dest" that is larger than
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the front of "src"; this is the next insertion
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position */
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dest_at = std::find_if(dest_at, dest_end, [&p, &src_front = *src_begin](const auto &i){
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return p(src_front, i);
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});
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if (dest_at == dest_end) {
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/* all items in "src" are larger than
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"this": splice the whole list at
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the end of "this" */
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dest.splice(dest_end, src);
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break;
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}
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/* find the first item of "src" that is not smaller
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than the "dest" insertion anchor; this is the end
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of the range of items to be spliced */
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const auto &dest_anchor = *dest_at;
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typename List::size_type n = 1;
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auto src_until = std::next(src_begin);
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while (src_until != src_end && p(*src_until, dest_anchor)) {
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++src_until;
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++n;
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}
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dest.splice(dest_at, src, src_begin, src_until, n);
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}
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}
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template<typename List>
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constexpr void
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SortList(List &list,
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std::predicate <typename List::const_reference, typename List::const_reference> auto p) noexcept
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{
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using std::swap;
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if (list.empty())
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return;
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/* bottom-up merge sort */
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List carry;
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StaticVector<List, 64> array;
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while (!list.empty()) {
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carry.splice(carry.begin(), list, list.begin());
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std::size_t i = 0;
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while (i < array.size() && !array[i].empty()) {
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auto &c = array[i++];
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MergeList(c, carry, p);
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swap(carry, c);
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}
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if (i == array.size())
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array.emplace_back();
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swap(carry, array[i]);
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}
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assert(!array.empty());
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for (std::size_t i = 1; i < array.size(); ++i)
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MergeList(array[i], array[i - 1], p);
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swap(list, array.back());
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}
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