@sussudio/base/common/skipList.mjs

Internal APIs for VS Code's utilities and user interface building blocks.

/*---------------------------------------------------------------------------------------------
 *  Copyright (c) Microsoft Corporation. All rights reserved.
 *  Licensed under the MIT License. See License.txt in the project root for license information.
 *--------------------------------------------------------------------------------------------*/
class Node {
	level;
	key;
	value;
	forward;
	constructor(level, key, value) {
		this.level = level;
		this.key = key;
		this.value = value;
		this.forward = [];
	}
}
const NIL = undefined;
export class SkipList {
	comparator;
	[Symbol.toStringTag] = 'SkipList';
	_maxLevel;
	_level = 0;
	_header;
	_size = 0;
	/**
	 *
	 * @param capacity Capacity at which the list performs best
	 */
	constructor(comparator, capacity = 2 ** 16) {
		this.comparator = comparator;
		this._maxLevel = Math.max(1, Math.log2(capacity) | 0);
		this._header = new Node(this._maxLevel, NIL, NIL);
	}
	get size() {
		return this._size;
	}
	clear() {
		this._header = new Node(this._maxLevel, NIL, NIL);
	}
	has(key) {
		return Boolean(SkipList._search(this, key, this.comparator));
	}
	get(key) {
		return SkipList._search(this, key, this.comparator)?.value;
	}
	set(key, value) {
		if (SkipList._insert(this, key, value, this.comparator)) {
			this._size += 1;
		}
		return this;
	}
	delete(key) {
		const didDelete = SkipList._delete(this, key, this.comparator);
		if (didDelete) {
			this._size -= 1;
		}
		return didDelete;
	}
	// --- iteration
	forEach(callbackfn, thisArg) {
		let node = this._header.forward[0];
		while (node) {
			callbackfn.call(thisArg, node.value, node.key, this);
			node = node.forward[0];
		}
	}
	[Symbol.iterator]() {
		return this.entries();
	}
	*entries() {
		let node = this._header.forward[0];
		while (node) {
			yield [node.key, node.value];
			node = node.forward[0];
		}
	}
	*keys() {
		let node = this._header.forward[0];
		while (node) {
			yield node.key;
			node = node.forward[0];
		}
	}
	*values() {
		let node = this._header.forward[0];
		while (node) {
			yield node.value;
			node = node.forward[0];
		}
	}
	toString() {
		// debug string...
		let result = '[SkipList]:';
		let node = this._header.forward[0];
		while (node) {
			result += `node(${node.key}, ${node.value}, lvl:${node.level})`;
			node = node.forward[0];
		}
		return result;
	}
	// from https://www.epaperpress.com/sortsearch/download/skiplist.pdf
	static _search(list, searchKey, comparator) {
		let x = list._header;
		for (let i = list._level - 1; i >= 0; i--) {
			while (x.forward[i] && comparator(x.forward[i].key, searchKey) < 0) {
				x = x.forward[i];
			}
		}
		x = x.forward[0];
		if (x && comparator(x.key, searchKey) === 0) {
			return x;
		}
		return undefined;
	}
	static _insert(list, searchKey, value, comparator) {
		const update = [];
		let x = list._header;
		for (let i = list._level - 1; i >= 0; i--) {
			while (x.forward[i] && comparator(x.forward[i].key, searchKey) < 0) {
				x = x.forward[i];
			}
			update[i] = x;
		}
		x = x.forward[0];
		if (x && comparator(x.key, searchKey) === 0) {
			// update
			x.value = value;
			return false;
		} else {
			// insert
			const lvl = SkipList._randomLevel(list);
			if (lvl > list._level) {
				for (let i = list._level; i < lvl; i++) {
					update[i] = list._header;
				}
				list._level = lvl;
			}
			x = new Node(lvl, searchKey, value);
			for (let i = 0; i < lvl; i++) {
				x.forward[i] = update[i].forward[i];
				update[i].forward[i] = x;
			}
			return true;
		}
	}
	static _randomLevel(list, p = 0.5) {
		let lvl = 1;
		while (Math.random() < p && lvl < list._maxLevel) {
			lvl += 1;
		}
		return lvl;
	}
	static _delete(list, searchKey, comparator) {
		const update = [];
		let x = list._header;
		for (let i = list._level - 1; i >= 0; i--) {
			while (x.forward[i] && comparator(x.forward[i].key, searchKey) < 0) {
				x = x.forward[i];
			}
			update[i] = x;
		}
		x = x.forward[0];
		if (!x || comparator(x.key, searchKey) !== 0) {
			// not found
			return false;
		}
		for (let i = 0; i < list._level; i++) {
			if (update[i].forward[i] !== x) {
				break;
			}
			update[i].forward[i] = x.forward[i];
		}
		while (list._level > 0 && list._header.forward[list._level - 1] === NIL) {
			list._level -= 1;
		}
		return true;
	}
}