ladybird/AK/RedBlackTree.h

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/*
* Copyright (c) 2021, Idan Horowitz <idan.horowitz@serenityos.org>
*
* SPDX-License-Identifier: BSD-2-Clause
*/
#pragma once
#include <AK/Concepts.h>
namespace AK {
template<Integral K>
class BaseRedBlackTree {
public:
[[nodiscard]] size_t size() const { return m_size; }
[[nodiscard]] bool is_empty() const { return m_size == 0; }
enum class Color : bool {
Red,
Black
};
struct Node {
Node* left_child { nullptr };
Node* right_child { nullptr };
Node* parent { nullptr };
Color color { Color::Red };
K key;
Node(K key)
: key(key)
{
}
virtual ~Node() {};
};
protected:
BaseRedBlackTree() = default; // These are protected to ensure no one instantiates the leaky base red black tree directly
virtual ~BaseRedBlackTree() {};
void rotate_left(Node* subtree_root)
{
VERIFY(subtree_root);
auto* pivot = subtree_root->right_child;
VERIFY(pivot);
auto* parent = subtree_root->parent;
// stage 1 - subtree_root's right child is now pivot's left child
subtree_root->right_child = pivot->left_child;
if (subtree_root->right_child)
subtree_root->right_child->parent = subtree_root;
// stage 2 - pivot's left child is now subtree_root
pivot->left_child = subtree_root;
subtree_root->parent = pivot;
// stage 3 - update pivot's parent
pivot->parent = parent;
if (!parent) { // new root
m_root = pivot;
} else if (parent->left_child == subtree_root) { // we are the left child
parent->left_child = pivot;
} else { // we are the right child
parent->right_child = pivot;
}
}
void rotate_right(Node* subtree_root)
{
VERIFY(subtree_root);
auto* pivot = subtree_root->left_child;
VERIFY(pivot);
auto* parent = subtree_root->parent;
// stage 1 - subtree_root's left child is now pivot's right child
subtree_root->left_child = pivot->right_child;
if (subtree_root->left_child)
subtree_root->left_child->parent = subtree_root;
// stage 2 - pivot's right child is now subtree_root
pivot->right_child = subtree_root;
subtree_root->parent = pivot;
// stage 3 - update pivot's parent
pivot->parent = parent;
if (!parent) { // new root
m_root = pivot;
} else if (parent->left_child == subtree_root) { // we are the left child
parent->left_child = pivot;
} else { // we are the right child
parent->right_child = pivot;
}
}
static Node* find(Node* node, K key)
{
while (node && node->key != key) {
if (key < node->key) {
node = node->left_child;
} else {
node = node->right_child;
}
}
return node;
}
static Node* find_largest_not_above(Node* node, K key)
{
Node* candidate = nullptr;
while (node) {
if (key == node->key) {
return node;
} else if (key < node->key) {
node = node->left_child;
} else {
candidate = node;
node = node->right_child;
}
}
return candidate;
}
void insert(Node* node)
{
VERIFY(node);
Node* parent = nullptr;
Node* temp = m_root;
while (temp) {
parent = temp;
if (node->key < temp->key) {
temp = temp->left_child;
} else {
temp = temp->right_child;
}
}
if (!parent) { // new root
node->color = Color::Black;
m_root = node;
m_size = 1;
m_minimum = node;
return;
} else if (node->key < parent->key) { // we are the left child
parent->left_child = node;
} else { // we are the right child
parent->right_child = node;
}
node->parent = parent;
if (node->parent->parent) // no fixups to be done for a height <= 2 tree
insert_fixups(node);
m_size++;
if (m_minimum->left_child == node)
m_minimum = node;
}
void insert_fixups(Node* node)
{
VERIFY(node && node->color == Color::Red);
while (node->parent && node->parent->color == Color::Red) {
auto* grand_parent = node->parent->parent;
if (grand_parent->right_child == node->parent) {
auto* uncle = grand_parent->left_child;
if (uncle && uncle->color == Color::Red) {
node->parent->color = Color::Black;
uncle->color = Color::Black;
grand_parent->color = Color::Red;
node = grand_parent;
} else {
if (node->parent->left_child == node) {
node = node->parent;
rotate_right(node);
}
node->parent->color = Color::Black;
grand_parent->color = Color::Red;
rotate_left(grand_parent);
}
} else {
auto* uncle = grand_parent->right_child;
if (uncle && uncle->color == Color::Red) {
node->parent->color = Color::Black;
uncle->color = Color::Black;
grand_parent->color = Color::Red;
node = grand_parent;
} else {
if (node->parent->right_child == node) {
node = node->parent;
rotate_left(node);
}
node->parent->color = Color::Black;
grand_parent->color = Color::Red;
rotate_right(grand_parent);
}
}
}
m_root->color = Color::Black; // the root should always be black
}
void remove(Node* node)
{
VERIFY(node);
// special case: deleting the only node
if (m_size == 1) {
m_root = nullptr;
m_size = 0;
return;
}
if (m_minimum == node)
m_minimum = successor(node);
// removal assumes the node has 0 or 1 child, so if we have 2, relink with the successor first (by definition the successor has no left child)
2021-04-18 08:30:03 +00:00
// FIXME: since we dont know how a value is represented in the node, we can't simply swap the values and keys, and instead we relink the nodes
// in place, this is quite a bit more expensive, as well as much less readable, is there a better way?
if (node->left_child && node->right_child) {
auto* successor_node = successor(node); // this is always non-null as all nodes besides the maximum node have a successor, and the maximum node has no right child
auto neighbour_swap = successor_node->parent == node;
node->left_child->parent = successor_node;
if (!neighbour_swap)
node->right_child->parent = successor_node;
if (node->parent) {
if (node->parent->left_child == node) {
node->parent->left_child = successor_node;
} else {
node->parent->right_child = successor_node;
}
} else {
m_root = successor_node;
}
if (successor_node->right_child)
successor_node->right_child->parent = node;
if (neighbour_swap) {
successor_node->parent = node->parent;
node->parent = successor_node;
} else {
if (successor_node->parent) {
if (successor_node->parent->left_child == successor_node) {
successor_node->parent->left_child = node;
} else {
successor_node->parent->right_child = node;
}
} else {
m_root = node;
}
swap(node->parent, successor_node->parent);
}
swap(node->left_child, successor_node->left_child);
if (neighbour_swap) {
node->right_child = successor_node->right_child;
successor_node->right_child = node;
} else {
swap(node->right_child, successor_node->right_child);
}
swap(node->color, successor_node->color);
}
auto* child = node->left_child ?: node->right_child;
if (child)
child->parent = node->parent;
if (node->parent) {
if (node->parent->left_child == node)
node->parent->left_child = child;
else
node->parent->right_child = child;
} else {
m_root = child;
}
// if the node is red then child must be black, and just replacing the node with its child should result in a valid tree (no change to black height)
if (node->color != Color::Red)
remove_fixups(child, node->parent);
m_size--;
}
// We maintain parent as a separate argument since node might be null
void remove_fixups(Node* node, Node* parent)
{
while (node != m_root && (!node || node->color == Color::Black)) {
if (parent->left_child == node) {
auto* sibling = parent->right_child;
if (sibling->color == Color::Red) {
sibling->color = Color::Black;
parent->color = Color::Red;
rotate_left(parent);
sibling = parent->right_child;
}
if ((!sibling->left_child || sibling->left_child->color == Color::Black) && (!sibling->right_child || sibling->right_child->color == Color::Black)) {
sibling->color = Color::Red;
node = parent;
} else {
if (!sibling->right_child || sibling->right_child->color == Color::Black) {
sibling->left_child->color = Color::Black; // null check?
sibling->color = Color::Red;
rotate_right(sibling);
sibling = parent->right_child;
}
sibling->color = parent->color;
parent->color = Color::Black;
sibling->right_child->color = Color::Black; // null check?
rotate_left(parent);
node = m_root; // fixed
}
} else {
auto* sibling = parent->left_child;
if (sibling->color == Color::Red) {
sibling->color = Color::Black;
parent->color = Color::Red;
rotate_right(parent);
sibling = parent->left_child;
}
if ((!sibling->left_child || sibling->left_child->color == Color::Black) && (!sibling->right_child || sibling->right_child->color == Color::Black)) {
sibling->color = Color::Red;
node = parent;
} else {
if (!sibling->left_child || sibling->left_child->color == Color::Black) {
sibling->right_child->color = Color::Black; // null check?
sibling->color = Color::Red;
rotate_left(sibling);
sibling = parent->left_child;
}
sibling->color = parent->color;
parent->color = Color::Black;
sibling->left_child->color = Color::Black; // null check?
rotate_right(parent);
node = m_root; // fixed
}
}
parent = node->parent;
}
2021-04-18 08:30:03 +00:00
node->color = Color::Black; // by this point node can't be null
}
static Node* successor(Node* node)
{
VERIFY(node);
if (node->right_child) {
node = node->right_child;
while (node->left_child)
node = node->left_child;
return node;
} else {
auto temp = node->parent;
while (temp && node == temp->right_child) {
node = temp;
temp = temp->parent;
}
return temp;
}
}
static Node* predecessor(Node* node)
{
VERIFY(node);
if (node->left_child) {
node = node->left_child;
while (node->right_child)
node = node->right_child;
return node;
} else {
auto temp = node->parent;
while (temp && node == temp->left_child) {
node = temp;
temp = temp->parent;
}
return temp;
}
}
Node* m_root { nullptr };
size_t m_size { 0 };
Node* m_minimum { nullptr }; // maintained for O(1) begin()
};
template<typename TreeType, typename ElementType>
class RedBlackTreeIterator {
public:
RedBlackTreeIterator() = default;
bool operator!=(const RedBlackTreeIterator& other) const { return m_node != other.m_node; }
RedBlackTreeIterator& operator++()
{
if (!m_node)
return *this;
m_prev = m_node;
// the complexity is O(logn) for each successor call, but the total complexity for all elements comes out to O(n), meaning the amortized cost for a single call is O(1)
m_node = static_cast<typename TreeType::Node*>(TreeType::successor(m_node));
return *this;
}
RedBlackTreeIterator& operator--()
{
if (!m_prev)
return *this;
m_node = m_prev;
m_prev = static_cast<typename TreeType::Node*>(TreeType::predecessor(m_prev));
return *this;
}
ElementType& operator*() { return m_node->value; }
ElementType* operator->() { return &m_node->value; }
[[nodiscard]] bool is_end() const { return !m_node; }
[[nodiscard]] bool is_begin() const { return !m_prev; }
private:
friend TreeType;
explicit RedBlackTreeIterator(typename TreeType::Node* node, typename TreeType::Node* prev = nullptr)
: m_node(node)
, m_prev(prev)
{
}
typename TreeType::Node* m_node { nullptr };
typename TreeType::Node* m_prev { nullptr };
};
template<Integral K, typename V>
class RedBlackTree : public BaseRedBlackTree<K> {
public:
RedBlackTree() = default;
virtual ~RedBlackTree() override
{
clear();
}
using BaseTree = BaseRedBlackTree<K>;
V* find(K key)
{
auto* node = static_cast<Node*>(BaseTree::find(this->m_root, key));
if (!node)
return nullptr;
return &node->value;
}
V* find_largest_not_above(K key)
{
auto* node = static_cast<Node*>(BaseTree::find_largest_not_above(this->m_root, key));
if (!node)
return nullptr;
return &node->value;
}
void insert(K key, const V& value)
{
insert(key, V(value));
}
void insert(K key, V&& value)
{
auto* node = new Node(key, move(value));
BaseTree::insert(node);
}
using Iterator = RedBlackTreeIterator<RedBlackTree, V>;
friend Iterator;
Iterator begin() { return Iterator(static_cast<Node*>(this->m_minimum)); }
Iterator end() { return {}; }
Iterator begin_from(K key) { return Iterator(static_cast<Node*>(BaseTree::find(this->m_root, key))); }
using ConstIterator = RedBlackTreeIterator<const RedBlackTree, const V>;
friend ConstIterator;
ConstIterator begin() const { return ConstIterator(static_cast<Node*>(this->m_minimum)); }
ConstIterator end() const { return {}; }
ConstIterator begin_from(K key) const { return ConstIterator(static_cast<Node*>(BaseTree::find(this->m_root, key))); }
ConstIterator find_largest_not_above_iterator(K key) const
{
auto node = static_cast<Node*>(BaseTree::find_largest_not_above(this->m_root, key));
return ConstIterator(node, static_cast<Node*>(BaseTree::predecessor(node)));
}
V unsafe_remove(K key)
{
auto* node = BaseTree::find(this->m_root, key);
VERIFY(node);
BaseTree::remove(node);
V temp = move(static_cast<Node*>(node)->value);
node->right_child = nullptr;
node->left_child = nullptr;
delete node;
return temp;
}
bool remove(K key)
{
auto* node = BaseTree::find(this->m_root, key);
if (!node)
return false;
BaseTree::remove(node);
node->right_child = nullptr;
node->left_child = nullptr;
delete node;
return true;
}
void clear()
{
if (this->m_root) {
delete this->m_root;
this->m_root = nullptr;
}
this->m_minimum = nullptr;
this->m_size = 0;
}
private:
struct Node : BaseRedBlackTree<K>::Node {
V value;
Node(K key, V value)
: BaseRedBlackTree<K>::Node(key)
, value(move(value))
{
}
~Node()
{
if (this->left_child)
delete this->left_child;
if (this->right_child)
delete this->right_child;
}
};
};
}
using AK::RedBlackTree;