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