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AK: Introduce cutoff to insertion sort for Quicksort

Implement insertion sort in AK. The cutoff value 7 is a magic number
here, values [5, 15] should work well. Main idea of the cutoff is to
reduce recursion performed by quicksort to speed up sorting
of small partitions.
This commit is contained in:
Marc Luqué 2022-03-25 17:06:11 +01:00 committed by Linus Groh
parent bbb256e8b5
commit 22f472249d
4 changed files with 119 additions and 0 deletions

45
AK/InsertionSort.h Normal file
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/*
* Copyright (c) 2022, Marc Luqué <marc.luque@outlook.com>
*
* SPDX-License-Identifier: BSD-2-Clause
*/
#pragma once
#include <AK/Concepts.h>
#include <AK/StdLibExtras.h>
namespace AK {
// Standard Insertion Sort, with `end` inclusive!
template<typename Collection, typename Comparator, typename T = decltype(declval<Collection>()[declval<int>()])>
void insertion_sort(Collection& col, ssize_t start, ssize_t end, Comparator comparator)
requires(Indexable<Collection, T>)
{
for (ssize_t i = start + 1; i <= end; ++i) {
for (ssize_t j = i; j > 0 && comparator(col[j], col[j - 1]); --j)
swap(col[j], col[j - 1]);
}
}
template<typename Collection, typename Comparator, typename T = decltype(declval<Collection>()[declval<int>()])>
void insertion_sort(Collection& collection, Comparator comparator)
requires(Indexable<Collection, T>)
{
if (collection.size() == 0)
return;
insertion_sort(collection, 0, collection.size() - 1, move(comparator));
}
template<typename Collection, typename T = decltype(declval<Collection>()[declval<int>()])>
void insertion_sort(Collection& collection)
requires(Indexable<Collection, T>)
{
if (collection.size() == 0)
return;
insertion_sort(collection, 0, collection.size() - 1, [](auto& a, auto& b) { return a < b; });
}
}
using AK::insertion_sort;