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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.
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sideshowbarker
2024-07-17 08:55:54 +09:00
Author: https://github.com/marcluque 🔰 Commit: https://github.com/SerenityOS/serenity/commit/22f472249d Pull-request: https://github.com/SerenityOS/serenity/pull/15992 Reviewed-by: https://github.com/ADKaster ✅ Reviewed-by: https://github.com/TobyAsE Reviewed-by: https://github.com/idispatch ✅ Reviewed-by: https://github.com/kleinesfilmroellchen
45
AK/InsertionSort.h
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45
AK/InsertionSort.h
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@ -0,0 +1,45 @@
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/*
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* Copyright (c) 2022, Marc Luqué <marc.luque@outlook.com>
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*
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* SPDX-License-Identifier: BSD-2-Clause
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*/
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#pragma once
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#include <AK/Concepts.h>
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#include <AK/StdLibExtras.h>
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namespace AK {
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// Standard Insertion Sort, with `end` inclusive!
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template<typename Collection, typename Comparator, typename T = decltype(declval<Collection>()[declval<int>()])>
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void insertion_sort(Collection& col, ssize_t start, ssize_t end, Comparator comparator)
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requires(Indexable<Collection, T>)
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{
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for (ssize_t i = start + 1; i <= end; ++i) {
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for (ssize_t j = i; j > 0 && comparator(col[j], col[j - 1]); --j)
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swap(col[j], col[j - 1]);
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}
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}
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template<typename Collection, typename Comparator, typename T = decltype(declval<Collection>()[declval<int>()])>
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void insertion_sort(Collection& collection, Comparator comparator)
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requires(Indexable<Collection, T>)
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{
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if (collection.size() == 0)
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return;
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insertion_sort(collection, 0, collection.size() - 1, move(comparator));
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}
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template<typename Collection, typename T = decltype(declval<Collection>()[declval<int>()])>
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void insertion_sort(Collection& collection)
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requires(Indexable<Collection, T>)
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{
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if (collection.size() == 0)
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return;
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insertion_sort(collection, 0, collection.size() - 1, [](auto& a, auto& b) { return a < b; });
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}
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}
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using AK::insertion_sort;
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@ -1,11 +1,13 @@
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/*
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/*
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* Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
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* Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
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* Copyright (c) 2022, Marc Luqué <marc.luque@outlook.com>
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*
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*
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* SPDX-License-Identifier: BSD-2-Clause
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* SPDX-License-Identifier: BSD-2-Clause
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*/
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*/
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#pragma once
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#pragma once
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#include <AK/InsertionSort.h>
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#include <AK/StdLibExtras.h>
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#include <AK/StdLibExtras.h>
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namespace AK {
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namespace AK {
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@ -14,10 +16,24 @@ namespace AK {
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* pivot quick_sort below. The other quick_sort below should only be used when
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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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* 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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* to the container itself.
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*
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* We use a cutoff to insertion sort for partitions of size 7 or smaller.
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* The idea is to avoid recursion for small partitions.
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* The value 7 here is a magic number. According to princeton's CS algorithm class
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* a value between 5 and 15 should work well in most situations:
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* https://algs4.cs.princeton.edu/23quicksort/
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*/
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*/
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static constexpr int INSERTION_SORT_CUTOFF = 7;
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template<typename Collection, typename LessThan>
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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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void dual_pivot_quick_sort(Collection& col, int start, int end, LessThan less_than)
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{
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{
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if ((end + 1) - start <= INSERTION_SORT_CUTOFF) {
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AK::insertion_sort(col, start, end, less_than);
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return;
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}
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while (start < end) {
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while (start < end) {
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int size = end - start + 1;
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int size = end - start + 1;
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if (size > 3) {
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if (size > 3) {
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@ -38,6 +38,7 @@ set(AK_TEST_SOURCES
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TestIPv4Address.cpp
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TestIPv4Address.cpp
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TestIPv6Address.cpp
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TestIPv6Address.cpp
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TestIndexSequence.cpp
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TestIndexSequence.cpp
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TestInsertionSort.cpp
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TestIntegerMath.cpp
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TestIntegerMath.cpp
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TestIntrusiveList.cpp
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TestIntrusiveList.cpp
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TestIntrusiveRedBlackTree.cpp
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TestIntrusiveRedBlackTree.cpp
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57
Tests/AK/TestInsertionSort.cpp
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57
Tests/AK/TestInsertionSort.cpp
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/*
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* Copyright (c) 2022, Marc Luqué <marc.luque@outlook.com>
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*
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* SPDX-License-Identifier: BSD-2-Clause
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*/
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#include <LibTest/TestCase.h>
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#include <AK/InsertionSort.h>
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#include <AK/Random.h>
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#include <AK/Vector.h>
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static constexpr int const n = 10;
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static constexpr int const iterations = 10;
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static constexpr int const seed = 1337;
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TEST_CASE(sorts_ascending)
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{
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srand(seed);
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for (int i = 0; i < iterations; ++i) {
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Vector<int, n> ints;
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for (int j = 0; j < n; ++j)
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ints.append(get_random<int>());
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Vector<int, n> ints_copy = ints;
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insertion_sort(ints);
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insertion_sort(ints_copy);
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for (int j = 0; j < n - 1; ++j) {
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EXPECT(ints[j] <= ints[j + 1]);
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EXPECT_EQ(ints[j], ints_copy[j]);
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EXPECT_EQ(ints[j + 1], ints_copy[j + 1]);
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}
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}
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}
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TEST_CASE(sorts_decending)
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{
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srand(seed);
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for (int i = 0; i < iterations; ++i) {
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Vector<int, n> ints;
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for (int j = 0; j < n; ++j)
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ints.append(get_random<int>());
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Vector<int, n> ints_copy = ints;
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insertion_sort(ints, [](auto& a, auto& b) { return a > b; });
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insertion_sort(ints_copy, [](auto& a, auto& b) { return a > b; });
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for (int j = 0; j < n - 1; ++j) {
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EXPECT(ints[j] >= ints[j + 1]);
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EXPECT_EQ(ints[j], ints_copy[j]);
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EXPECT_EQ(ints[j + 1], ints_copy[j + 1]);
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}
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}
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}
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