godot/core/templates/rb_set.h

/*************************************************************************/
/*  rb_set.h                                                             */
/*************************************************************************/
/*                       This file is part of:                           */
/*                           GODOT ENGINE                                */
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/* Copyright (c) 2007-2022 Juan Linietsky, Ariel Manzur.                 */
/* Copyright (c) 2014-2022 Godot Engine contributors (cf. AUTHORS.md).   */
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/* a copy of this software and associated documentation files (the       */
/* "Software"), to deal in the Software without restriction, including   */
/* without limitation the rights to use, copy, modify, merge, publish,   */
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/*************************************************************************/

#ifndef RB_SET_H
#define RB_SET_H

#include "core/os/memory.h"
#include "core/typedefs.h"

// based on the very nice implementation of rb-trees by:
// https://web.archive.org/web/20120507164830/https://web.mit.edu/~emin/www/source_code/red_black_tree/index.html

template <class T, class C = Comparator<T>, class A = DefaultAllocator>
class RBSet {
	enum Color {
		RED,
		BLACK
	};
	struct _Data;

public:
	class Element {
	private:
		friend class RBSet<T, C, A>;
		int color = RED;
		Element *right = nullptr;
		Element *left = nullptr;
		Element *parent = nullptr;
		Element *_next = nullptr;
		Element *_prev = nullptr;
		T value;
		//_Data *data;

	public:
		const Element *next() const {
			return _next;
		}
		Element *next() {
			return _next;
		}
		const Element *prev() const {
			return _prev;
		}
		Element *prev() {
			return _prev;
		}
		T &get() {
			return value;
		}
		const T &get() const {
			return value;
		};
		Element() {}
	};

	typedef T ValueType;

	struct Iterator {
		_FORCE_INLINE_ T &operator*() const {
			return E->get();
		}
		_FORCE_INLINE_ T *operator->() const { return &E->get(); }
		_FORCE_INLINE_ Iterator &operator++() {
			E = E->next();
			return *this;
		}
		_FORCE_INLINE_ Iterator &operator--() {
			E = E->prev();
			return *this;
		}

		_FORCE_INLINE_ bool operator==(const Iterator &b) const { return E == b.E; }
		_FORCE_INLINE_ bool operator!=(const Iterator &b) const { return E != b.E; }

		explicit operator bool() const { return E != nullptr; }
		Iterator(Element *p_E) { E = p_E; }
		Iterator() {}
		Iterator(const Iterator &p_it) { E = p_it.E; }

	private:
		Element *E = nullptr;
	};

	struct ConstIterator {
		_FORCE_INLINE_ const T &operator*() const {
			return E->get();
		}
		_FORCE_INLINE_ const T *operator->() const { return &E->get(); }
		_FORCE_INLINE_ ConstIterator &operator++() {
			E = E->next();
			return *this;
		}
		_FORCE_INLINE_ ConstIterator &operator--() {
			E = E->prev();
			return *this;
		}

		_FORCE_INLINE_ bool operator==(const ConstIterator &b) const { return E == b.E; }
		_FORCE_INLINE_ bool operator!=(const ConstIterator &b) const { return E != b.E; }

		_FORCE_INLINE_ ConstIterator(const Element *p_E) { E = p_E; }
		_FORCE_INLINE_ ConstIterator() {}
		_FORCE_INLINE_ ConstIterator(const ConstIterator &p_it) { E = p_it.E; }

		explicit operator bool() const { return E != nullptr; }

	private:
		const Element *E = nullptr;
	};

	_FORCE_INLINE_ Iterator begin() {
		return Iterator(front());
	}
	_FORCE_INLINE_ Iterator end() {
		return Iterator(nullptr);
	}

#if 0
	//to use when replacing find()
	_FORCE_INLINE_ Iterator find(const K &p_key) {
		return Iterator(find(p_key));
	}
#endif

	_FORCE_INLINE_ ConstIterator begin() const {
		return ConstIterator(front());
	}
	_FORCE_INLINE_ ConstIterator end() const {
		return ConstIterator(nullptr);
	}

#if 0
	//to use when replacing find()
	_FORCE_INLINE_ ConstIterator find(const K &p_key) const {
		return ConstIterator(find(p_key));
	}
#endif
private:
	struct _Data {
		Element *_root = nullptr;
		Element *_nil = nullptr;
		int size_cache = 0;

		_FORCE_INLINE_ _Data() {
#ifdef GLOBALNIL_DISABLED
			_nil = memnew_allocator(Element, A);
			_nil->parent = _nil->left = _nil->right = _nil;
			_nil->color = BLACK;
#else
			_nil = (Element *)&_GlobalNilClass::_nil;
#endif
		}

		void _create_root() {
			_root = memnew_allocator(Element, A);
			_root->parent = _root->left = _root->right = _nil;
			_root->color = BLACK;
		}

		void _free_root() {
			if (_root) {
				memdelete_allocator<Element, A>(_root);
				_root = nullptr;
			}
		}

		~_Data() {
			_free_root();

#ifdef GLOBALNIL_DISABLED
			memdelete_allocator<Element, A>(_nil);
#endif
		}
	};

	_Data _data;

	inline void _set_color(Element *p_node, int p_color) {
		ERR_FAIL_COND(p_node == _data._nil && p_color == RED);
		p_node->color = p_color;
	}

	inline void _rotate_left(Element *p_node) {
		Element *r = p_node->right;
		p_node->right = r->left;
		if (r->left != _data._nil) {
			r->left->parent = p_node;
		}
		r->parent = p_node->parent;
		if (p_node == p_node->parent->left) {
			p_node->parent->left = r;
		} else {
			p_node->parent->right = r;
		}

		r->left = p_node;
		p_node->parent = r;
	}

	inline void _rotate_right(Element *p_node) {
		Element *l = p_node->left;
		p_node->left = l->right;
		if (l->right != _data._nil) {
			l->right->parent = p_node;
		}
		l->parent = p_node->parent;
		if (p_node == p_node->parent->right) {
			p_node->parent->right = l;
		} else {
			p_node->parent->left = l;
		}

		l->right = p_node;
		p_node->parent = l;
	}

	inline Element *_successor(Element *p_node) const {
		Element *node = p_node;

		if (node->right != _data._nil) {
			node = node->right;
			while (node->left != _data._nil) { /* returns the minimum of the right subtree of node */
				node = node->left;
			}
			return node;
		} else {
			while (node == node->parent->right) {
				node = node->parent;
			}

			if (node->parent == _data._root) {
				return nullptr; // No successor, as p_node = last node
			}
			return node->parent;
		}
	}

	inline Element *_predecessor(Element *p_node) const {
		Element *node = p_node;

		if (node->left != _data._nil) {
			node = node->left;
			while (node->right != _data._nil) { /* returns the minimum of the left subtree of node */
				node = node->right;
			}
			return node;
		} else {
			while (node == node->parent->left) {
				node = node->parent;
			}

			if (node == _data._root) {
				return nullptr; // No predecessor, as p_node = first node.
			}
			return node->parent;
		}
	}

	Element *_find(const T &p_value) const {
		Element *node = _data._root->left;
		C less;

		while (node != _data._nil) {
			if (less(p_value, node->value)) {
				node = node->left;
			} else if (less(node->value, p_value)) {
				node = node->right;
			} else {
				return node; // found
			}
		}

		return nullptr;
	}

	Element *_lower_bound(const T &p_value) const {
		Element *node = _data._root->left;
		Element *prev = nullptr;
		C less;

		while (node != _data._nil) {
			prev = node;

			if (less(p_value, node->value)) {
				node = node->left;
			} else if (less(node->value, p_value)) {
				node = node->right;
			} else {
				return node; // found
			}
		}

		if (prev == nullptr) {
			return nullptr; // tree empty
		}

		if (less(prev->value, p_value)) {
			prev = prev->_next;
		}

		return prev;
	}

	void _insert_rb_fix(Element *p_new_node) {
		Element *node = p_new_node;
		Element *nparent = node->parent;
		Element *ngrand_parent = nullptr;

		while (nparent->color == RED) {
			ngrand_parent = nparent->parent;

			if (nparent == ngrand_parent->left) {
				if (ngrand_parent->right->color == RED) {
					_set_color(nparent, BLACK);
					_set_color(ngrand_parent->right, BLACK);
					_set_color(ngrand_parent, RED);
					node = ngrand_parent;
					nparent = node->parent;
				} else {
					if (node == nparent->right) {
						_rotate_left(nparent);
						node = nparent;
						nparent = node->parent;
					}
					_set_color(nparent, BLACK);
					_set_color(ngrand_parent, RED);
					_rotate_right(ngrand_parent);
				}
			} else {
				if (ngrand_parent->left->color == RED) {
					_set_color(nparent, BLACK);
					_set_color(ngrand_parent->left, BLACK);
					_set_color(ngrand_parent, RED);
					node = ngrand_parent;
					nparent = node->parent;
				} else {
					if (node == nparent->left) {
						_rotate_right(nparent);
						node = nparent;
						nparent = node->parent;
					}
					_set_color(nparent, BLACK);
					_set_color(ngrand_parent, RED);
					_rotate_left(ngrand_parent);
				}
			}
		}

		_set_color(_data._root->left, BLACK);
	}

	Element *_insert(const T &p_value) {
		Element *new_parent = _data._root;
		Element *node = _data._root->left;
		C less;

		while (node != _data._nil) {
			new_parent = node;

			if (less(p_value, node->value)) {
				node = node->left;
			} else if (less(node->value, p_value)) {
				node = node->right;
			} else {
				return node; // Return existing node
			}
		}

		Element *new_node = memnew_allocator(Element, A);
		new_node->parent = new_parent;
		new_node->right = _data._nil;
		new_node->left = _data._nil;
		new_node->value = p_value;
		//new_node->data=_data;

		if (new_parent == _data._root || less(p_value, new_parent->value)) {
			new_parent->left = new_node;
		} else {
			new_parent->right = new_node;
		}

		new_node->_next = _successor(new_node);
		new_node->_prev = _predecessor(new_node);
		if (new_node->_next) {
			new_node->_next->_prev = new_node;
		}
		if (new_node->_prev) {
			new_node->_prev->_next = new_node;
		}

		_data.size_cache++;
		_insert_rb_fix(new_node);
		return new_node;
	}

	void _erase_fix_rb(Element *p_node) {
		Element *root = _data._root->left;
		Element *node = _data._nil;
		Element *sibling = p_node;
		Element *parent = sibling->parent;

		while (node != root) { // If red node found, will exit at a break
			if (sibling->color == RED) {
				_set_color(sibling, BLACK);
				_set_color(parent, RED);
				if (sibling == parent->right) {
					sibling = sibling->left;
					_rotate_left(parent);
				} else {
					sibling = sibling->right;
					_rotate_right(parent);
				}
			}
			if ((sibling->left->color == BLACK) && (sibling->right->color == BLACK)) {
				_set_color(sibling, RED);
				if (parent->color == RED) {
					_set_color(parent, BLACK);
					break;
				} else { // loop: haven't found any red nodes yet
					node = parent;
					parent = node->parent;
					sibling = (node == parent->left) ? parent->right : parent->left;
				}
			} else {
				if (sibling == parent->right) {
					if (sibling->right->color == BLACK) {
						_set_color(sibling->left, BLACK);
						_set_color(sibling, RED);
						_rotate_right(sibling);
						sibling = sibling->parent;
					}
					_set_color(sibling, parent->color);
					_set_color(parent, BLACK);
					_set_color(sibling->right, BLACK);
					_rotate_left(parent);
					break;
				} else {
					if (sibling->left->color == BLACK) {
						_set_color(sibling->right, BLACK);
						_set_color(sibling, RED);
						_rotate_left(sibling);
						sibling = sibling->parent;
					}

					_set_color(sibling, parent->color);
					_set_color(parent, BLACK);
					_set_color(sibling->left, BLACK);
					_rotate_right(parent);
					break;
				}
			}
		}

		ERR_FAIL_COND(_data._nil->color != BLACK);
	}

	void _erase(Element *p_node) {
		Element *rp = ((p_node->left == _data._nil) || (p_node->right == _data._nil)) ? p_node : p_node->_next;
		Element *node = (rp->left == _data._nil) ? rp->right : rp->left;

		Element *sibling = nullptr;
		if (rp == rp->parent->left) {
			rp->parent->left = node;
			sibling = rp->parent->right;
		} else {
			rp->parent->right = node;
			sibling = rp->parent->left;
		}

		if (node->color == RED) {
			node->parent = rp->parent;
			_set_color(node, BLACK);
		} else if (rp->color == BLACK && rp->parent != _data._root) {
			_erase_fix_rb(sibling);
		}

		if (rp != p_node) {
			ERR_FAIL_COND(rp == _data._nil);

			rp->left = p_node->left;
			rp->right = p_node->right;
			rp->parent = p_node->parent;
			rp->color = p_node->color;
			if (p_node->left != _data._nil) {
				p_node->left->parent = rp;
			}
			if (p_node->right != _data._nil) {
				p_node->right->parent = rp;
			}

			if (p_node == p_node->parent->left) {
				p_node->parent->left = rp;
			} else {
				p_node->parent->right = rp;
			}
		}

		if (p_node->_next) {
			p_node->_next->_prev = p_node->_prev;
		}
		if (p_node->_prev) {
			p_node->_prev->_next = p_node->_next;
		}

		memdelete_allocator<Element, A>(p_node);
		_data.size_cache--;
		ERR_FAIL_COND(_data._nil->color == RED);
	}

	void _calculate_depth(Element *p_element, int &max_d, int d) const {
		if (p_element == _data._nil) {
			return;
		}

		_calculate_depth(p_element->left, max_d, d + 1);
		_calculate_depth(p_element->right, max_d, d + 1);

		if (d > max_d) {
			max_d = d;
		}
	}

	void _cleanup_tree(Element *p_element) {
		if (p_element == _data._nil) {
			return;
		}

		_cleanup_tree(p_element->left);
		_cleanup_tree(p_element->right);
		memdelete_allocator<Element, A>(p_element);
	}

	void _copy_from(const RBSet &p_set) {
		clear();
		// not the fastest way, but safeset to write.
		for (Element *I = p_set.front(); I; I = I->next()) {
			insert(I->get());
		}
	}

public:
	const Element *find(const T &p_value) const {
		if (!_data._root) {
			return nullptr;
		}

		const Element *res = _find(p_value);
		return res;
	}

	Element *find(const T &p_value) {
		if (!_data._root) {
			return nullptr;
		}

		Element *res = _find(p_value);
		return res;
	}

	Element *lower_bound(const T &p_value) const {
		if (!_data._root) {
			return nullptr;
		}
		return _lower_bound(p_value);
	}

	bool has(const T &p_value) const {
		return find(p_value) != nullptr;
	}

	Element *insert(const T &p_value) {
		if (!_data._root) {
			_data._create_root();
		}
		return _insert(p_value);
	}

	void erase(Element *p_element) {
		if (!_data._root || !p_element) {
			return;
		}

		_erase(p_element);
		if (_data.size_cache == 0 && _data._root) {
			_data._free_root();
		}
	}

	bool erase(const T &p_value) {
		if (!_data._root) {
			return false;
		}

		Element *e = find(p_value);
		if (!e) {
			return false;
		}

		_erase(e);
		if (_data.size_cache == 0 && _data._root) {
			_data._free_root();
		}
		return true;
	}

	Element *front() const {
		if (!_data._root) {
			return nullptr;
		}

		Element *e = _data._root->left;
		if (e == _data._nil) {
			return nullptr;
		}

		while (e->left != _data._nil) {
			e = e->left;
		}

		return e;
	}

	Element *back() const {
		if (!_data._root) {
			return nullptr;
		}

		Element *e = _data._root->left;
		if (e == _data._nil) {
			return nullptr;
		}

		while (e->right != _data._nil) {
			e = e->right;
		}

		return e;
	}

	inline bool is_empty() const {
		return _data.size_cache == 0;
	}
	inline int size() const {
		return _data.size_cache;
	}

	int calculate_depth() const {
		// used for debug mostly
		if (!_data._root) {
			return 0;
		}

		int max_d = 0;
		_calculate_depth(_data._root->left, max_d, 0);
		return max_d;
	}

	void clear() {
		if (!_data._root) {
			return;
		}

		_cleanup_tree(_data._root->left);
		_data._root->left = _data._nil;
		_data.size_cache = 0;
		_data._free_root();
	}

	void operator=(const RBSet &p_set) {
		_copy_from(p_set);
	}

	RBSet(const RBSet &p_set) {
		_copy_from(p_set);
	}

	_FORCE_INLINE_ RBSet() {}

	~RBSet() {
		clear();
	}
};

#endif // RB_SET_H