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136 lines
4.1 KiB
C++
136 lines
4.1 KiB
C++
/*
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* Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
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* All rights reserved.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions are met:
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*
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* 1. Redistributions of source code must retain the above copyright notice, this
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* list of conditions and the following disclaimer.
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*
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* 2. Redistributions in binary form must reproduce the above copyright notice,
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* this list of conditions and the following disclaimer in the documentation
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* and/or other materials provided with the distribution.
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*
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* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
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* AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
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* DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
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* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
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* SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
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* CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
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* OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
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* OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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*/
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#pragma once
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#include <AK/StdLibExtras.h>
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namespace AK {
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/* This is a dual pivot quick sort. It is quite a bit faster than the single
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* pivot quick_sort below. The other quick_sort below should only be used when
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* you are stuck with simple iterators to a container and you don't have access
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* to the container itself.
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*/
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template<typename Collection, typename LessThan>
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void dual_pivot_quick_sort(Collection& col, int start, int end, LessThan less_than)
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{
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if (start >= end) {
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return;
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}
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int left_pointer, right_pointer;
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if (!less_than(col[start], col[end])) {
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swap(col[start], col[end]);
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}
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int j = start + 1;
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int k = start + 1;
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int g = end - 1;
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auto&& left_pivot = col[start];
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auto&& right_pivot = col[end];
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while (k <= g) {
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if (less_than(col[k], left_pivot)) {
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swap(col[k], col[j]);
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j++;
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} else if (!less_than(col[k], right_pivot)) {
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while (!less_than(col[g], right_pivot) && k < g) {
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g--;
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}
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swap(col[k], col[g]);
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g--;
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if (less_than(col[k], left_pivot)) {
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swap(col[k], col[j]);
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j++;
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}
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}
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k++;
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}
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j--;
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g++;
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swap(col[start], col[j]);
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swap(col[end], col[g]);
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left_pointer = j;
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right_pointer = g;
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dual_pivot_quick_sort(col, start, left_pointer - 1, less_than);
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dual_pivot_quick_sort(col, left_pointer + 1, right_pointer - 1, less_than);
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dual_pivot_quick_sort(col, right_pointer + 1, end, less_than);
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}
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template<typename Iterator, typename LessThan>
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void quick_sort(Iterator start, Iterator end, LessThan less_than)
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{
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int size = end - start;
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if (size <= 1)
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return;
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int pivot_point = size / 2;
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auto pivot = *(start + pivot_point);
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if (pivot_point)
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swap(*(start + pivot_point), *start);
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int i = 1;
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for (int j = 1; j < size; ++j) {
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if (less_than(*(start + j), pivot)) {
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swap(*(start + j), *(start + i));
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++i;
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}
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}
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swap(*start, *(start + i - 1));
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quick_sort(start, start + i - 1, less_than);
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quick_sort(start + i, end, less_than);
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}
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template<typename Iterator>
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void quick_sort(Iterator start, Iterator end)
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{
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quick_sort(start, end, [](auto& a, auto& b) { return a < b; });
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}
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template<typename Collection, typename LessThan>
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void quick_sort(Collection& collection, LessThan less_than)
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{
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dual_pivot_quick_sort(collection, 0, collection.size() - 1, move(less_than));
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}
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template<typename Collection>
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void quick_sort(Collection& collection)
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{
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dual_pivot_quick_sort(collection, 0, collection.size() - 1,
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[](auto& a, auto& b) { return a < b; });
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}
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}
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using AK::quick_sort;
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