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/*
* Copyright (c) 2021, Idan Horowitz <idan.horowitz@serenityos.org>
*
* SPDX-License-Identifier: BSD-2-Clause
*/
#pragma once
#include <AK/Types.h>
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;
for (size_t i = 0; i < size; i++) {
m_elements[i].key = keys[i];
m_elements[i].value = values[i];
}
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_elements[index].key = key;
m_elements[index].value = value;
heapify_up(index);
}
V pop_min()
{
VERIFY(!is_empty());
auto index = --m_size;
swap(m_elements[0], m_elements[index]);
heapify_down(0);
return m_elements[index].value;
}
const V& peek_min() const
{
VERIFY(!is_empty());
return m_elements[0].value;
}
const K& peek_min_key() const
{
VERIFY(!is_empty());
return m_elements[0].key;
}
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_elements[right_child].key < m_elements[min_child].key)
min_child = right_child;
if (m_elements[index].key <= m_elements[min_child].key)
break;
swap(m_elements[index], m_elements[min_child]);
index = min_child;
}
}
void heapify_up(size_t index)
{
while (index != 0) {
auto parent = (index - 1) / 2;
if (m_elements[index].key >= m_elements[parent].key)
break;
swap(m_elements[index], m_elements[parent]);
index = parent;
}
}
struct {
K key;
V value;
} m_elements[Capacity];
size_t m_size { 0 };
};
}
using AK::BinaryHeap;
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