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AK: Implement minimum BinaryHeap

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This enables efficient implementations of priority queues,
and will also be used in LibCompress for efficient huffman
tree generation.
This commit is contained in:
Idan Horowitz 2021-03-03 23:05:34 +02:00 committed by Andreas Kling
parent 0ddc0e45ae
commit 168cf6fac9
3 changed files with 218 additions and 0 deletions
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128
AK/BinaryHeap.h Normal file
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@ -0,0 +1,128 @@
/*
* Copyright (c) 2021, Idan Horowitz <idan.horowitz@gmail.com>
* 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
namespace AK {
template<typename K, typename V, size_t Capacity>
class BinaryHeap {
public:
BinaryHeap() = default;
~BinaryHeap() = default;
// This constructor allows for O(n) construction of the heap (instead of O(nlogn) for repeated insertions)
BinaryHeap(K keys[], V values[], size_t size)
{
VERIFY(size <= Capacity);
m_size = size;
__builtin_memcpy(m_keys, keys, size * sizeof(K));
__builtin_memcpy(m_values, values, size * sizeof(V));
for (ssize_t i = size / 2; i >= 0; i--) {
heapify_down(i);
}
}
[[nodiscard]] size_t size() const { return m_size; }
[[nodiscard]] bool is_empty() const { return m_size == 0; }
void insert(K key, V value)
{
VERIFY(m_size < Capacity);
auto index = m_size++;
m_keys[index] = key;
m_values[index] = value;
heapify_up(index);
}
V pop_min()
{
VERIFY(!is_empty());
auto index = --m_size;
swap(m_keys[0], m_keys[index]);
swap(m_values[0], m_values[index]);
heapify_down(0);
return m_values[index];
}
const V& peek_min() const
{
VERIFY(!is_empty());
return m_values[0];
}
const V& peek_min_key() const
{
VERIFY(!is_empty());
return m_keys[0];
}
void clear()
{
m_size = 0;
}
private:
void heapify_down(size_t index)
{
while (index * 2 + 1 < m_size) {
auto left_child = index * 2 + 1;
auto right_child = index * 2 + 2;
auto min_child = left_child;
if (right_child < m_size && m_keys[right_child] < m_keys[min_child])
min_child = right_child;
if (m_keys[index] <= m_keys[min_child])
break;
swap(m_keys[index], m_keys[min_child]);
swap(m_values[index], m_values[min_child]);
index = min_child;
}
}
void heapify_up(size_t index)
{
while (index != 0) {
auto parent = (index - 1) / 2;
if (m_keys[index] >= m_keys[parent])
break;
swap(m_keys[index], m_keys[parent]);
swap(m_values[index], m_values[parent]);
index = parent;
}
}
K m_keys[Capacity];
V m_values[Capacity];
size_t m_size { 0 };
};
}
using AK::BinaryHeap;

1
AK/Tests/CMakeLists.txt
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@ -7,6 +7,7 @@ set(AK_TEST_SOURCES
TestAtomic.cpp
TestBadge.cpp
TestBase64.cpp
TestBinaryHeap.cpp
TestBinarySearch.cpp
TestBitmap.cpp
TestByteBuffer.cpp

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AK/Tests/TestBinaryHeap.cpp Normal file
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/*
* Copyright (c) 2021, Idan Horowitz <idan.horowitz@gmail.com>
* 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.
*/
#include <AK/TestSuite.h>
#include <AK/BinaryHeap.h>
#include <AK/String.h>
TEST_CASE(construct)
{
BinaryHeap<int, int, 5> empty;
EXPECT(empty.is_empty());
EXPECT(empty.size() == 0);
}
TEST_CASE(construct_from_existing)
{
int keys[] = { 3, 2, 1 };
char values[] = { 'c', 'b', 'a' };
BinaryHeap<int, char, 5> from_existing(keys, values, 3);
EXPECT(from_existing.size() == 3);
EXPECT_EQ(from_existing.pop_min(), 'a');
EXPECT_EQ(from_existing.pop_min(), 'b');
EXPECT_EQ(from_existing.pop_min(), 'c');
}
TEST_CASE(populate_int)
{
BinaryHeap<int, int, 5> ints;
ints.insert(1, 10);
ints.insert(3, 20);
ints.insert(2, 30);
EXPECT_EQ(ints.size(), 3u);
EXPECT_EQ(ints.pop_min(), 10);
EXPECT_EQ(ints.size(), 2u);
EXPECT_EQ(ints.pop_min(), 30);
EXPECT_EQ(ints.size(), 1u);
EXPECT_EQ(ints.pop_min(), 20);
EXPECT_EQ(ints.size(), 0u);
}
TEST_CASE(populate_string)
{
BinaryHeap<int, String, 5> strings;
strings.insert(1, "ABC");
strings.insert(2, "DEF");
EXPECT_EQ(strings.size(), 2u);
EXPECT_EQ(strings.pop_min(), "ABC");
EXPECT_EQ(strings.pop_min(), "DEF");
EXPECT(strings.is_empty());
}
TEST_CASE(large_populate_reverse)
{
BinaryHeap<int, int, 1024> ints;
for (int i = 1023; i >= 0; i--) {
ints.insert(i, i);
}
EXPECT_EQ(ints.size(), 1024u);
for (int i = 0; i < 1024; i++) {
EXPECT_EQ(ints.peek_min(), i);
EXPECT_EQ(ints.pop_min(), i);
}
}
TEST_MAIN(BinaryHeap)