275 lines
7.0 KiB
JavaScript
275 lines
7.0 KiB
JavaScript
"use strict";
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// Simulations show these probabilities for a single change
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// 93.1% that one group is invalidated
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// 4.8% that two groups are invalidated
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// 1.1% that 3 groups are invalidated
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// 0.1% that 4 or more groups are invalidated
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//
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// And these for removing/adding 10 lexically adjacent files
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// 64.5% that one group is invalidated
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// 24.8% that two groups are invalidated
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// 7.8% that 3 groups are invalidated
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// 2.7% that 4 or more groups are invalidated
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//
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// And these for removing/adding 3 random files
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// 0% that one group is invalidated
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// 3.7% that two groups are invalidated
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// 80.8% that 3 groups are invalidated
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// 12.3% that 4 groups are invalidated
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// 3.2% that 5 or more groups are invalidated
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/**
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*
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* @param {string} a key
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* @param {string} b key
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* @returns {number} the similarity as number
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*/
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const similarity = (a, b) => {
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const l = Math.min(a.length, b.length);
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let dist = 0;
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for (let i = 0; i < l; i++) {
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const ca = a.charCodeAt(i);
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const cb = b.charCodeAt(i);
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dist += Math.max(0, 10 - Math.abs(ca - cb));
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}
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return dist;
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};
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/**
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* @param {string} a key
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* @param {string} b key
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* @returns {string} the common part and a single char for the difference
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*/
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const getName = (a, b) => {
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const l = Math.min(a.length, b.length);
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let r = "";
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for (let i = 0; i < l; i++) {
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const ca = a.charAt(i);
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const cb = b.charAt(i);
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r += ca;
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if (ca === cb) {
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continue;
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}
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return r;
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}
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return a;
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};
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/**
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* @template T
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*/
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class Node {
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/**
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* @param {T} item item
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* @param {string} key key
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* @param {number} size size
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*/
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constructor(item, key, size) {
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this.item = item;
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this.key = key;
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this.size = size;
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}
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}
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/**
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* @template T
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*/
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class Group {
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/**
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* @param {Node<T>[]} nodes nodes
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* @param {number[]} similarities similarities between the nodes (length = nodes.length - 1)
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*/
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constructor(nodes, similarities) {
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this.nodes = nodes;
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this.similarities = similarities;
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this.size = nodes.reduce((size, node) => size + node.size, 0);
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/** @type {string} */
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this.key = undefined;
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}
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}
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/**
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* @template T
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* @typedef {Object} GroupedItems<T>
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* @property {string} key
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* @property {T[]} items
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* @property {number} size
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*/
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/**
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* @template T
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* @typedef {Object} Options
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* @property {number} maxSize maximum size of a group
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* @property {number} minSize minimum size of a group (preferred over maximum size)
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* @property {Iterable<T>} items a list of items
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* @property {function(T): number} getSize function to get size of an item
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* @property {function(T): string} getKey function to get the key of an item
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*/
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/**
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* @template T
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* @param {Options<T>} options options object
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* @returns {GroupedItems<T>[]} grouped items
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*/
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module.exports = ({ maxSize, minSize, items, getSize, getKey }) => {
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/** @type {Group<T>[]} */
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const result = [];
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const nodes = Array.from(
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items,
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item => new Node(item, getKey(item), getSize(item))
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);
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/** @type {Node<T>[]} */
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const initialNodes = [];
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// lexically ordering of keys
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nodes.sort((a, b) => {
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if (a.key < b.key) return -1;
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if (a.key > b.key) return 1;
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return 0;
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});
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// return nodes bigger than maxSize directly as group
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for (const node of nodes) {
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if (node.size >= maxSize) {
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result.push(new Group([node], []));
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} else {
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initialNodes.push(node);
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}
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}
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if (initialNodes.length > 0) {
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// calculate similarities between lexically adjacent nodes
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/** @type {number[]} */
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const similarities = [];
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for (let i = 1; i < initialNodes.length; i++) {
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const a = initialNodes[i - 1];
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const b = initialNodes[i];
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similarities.push(similarity(a.key, b.key));
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}
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const initialGroup = new Group(initialNodes, similarities);
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if (initialGroup.size < minSize) {
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// We hit an edgecase where the working set is already smaller than minSize
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// We merge it with the smallest result node to keep minSize intact
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if (result.length > 0) {
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const smallestGroup = result.reduce(
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(min, group) => (min.size > group.size ? group : min)
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);
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for (const node of initialGroup.nodes) smallestGroup.nodes.push(node);
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smallestGroup.nodes.sort((a, b) => {
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if (a.key < b.key) return -1;
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if (a.key > b.key) return 1;
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return 0;
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});
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} else {
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// There are no other nodes
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// We use all nodes and have to accept that it's smaller than minSize
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result.push(initialGroup);
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}
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} else {
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const queue = [initialGroup];
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while (queue.length) {
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const group = queue.pop();
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// only groups bigger than maxSize need to be splitted
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if (group.size < maxSize) {
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result.push(group);
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continue;
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}
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// find unsplittable area from left and right
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// going minSize from left and right
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// at least one node need to be included otherwise we get stuck
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let left = 0;
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let leftSize = 0;
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while (leftSize <= minSize) {
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leftSize += group.nodes[left].size;
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left++;
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}
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let right = group.nodes.length - 1;
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let rightSize = 0;
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while (rightSize <= minSize) {
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rightSize += group.nodes[right].size;
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right--;
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}
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if (left - 1 > right) {
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// can't split group while holding minSize
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// because minSize is preferred of maxSize we return
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// the group here even while it's too big
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// To avoid this make sure maxSize > minSize * 3
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result.push(group);
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continue;
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}
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if (left <= right) {
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// when there is a area between left and right
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// we look for best split point
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// we split at the minimum similarity
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// here key space is separated the most
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let best = left - 1;
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let bestSimilarity = group.similarities[best];
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for (let i = left; i <= right; i++) {
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const similarity = group.similarities[i];
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if (similarity < bestSimilarity) {
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best = i;
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bestSimilarity = similarity;
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}
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}
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left = best + 1;
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right = best;
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}
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// create two new groups for left and right area
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// and queue them up
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const rightNodes = [group.nodes[right + 1]];
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/** @type {number[]} */
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const rightSimilaries = [];
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for (let i = right + 2; i < group.nodes.length; i++) {
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rightSimilaries.push(group.similarities[i - 1]);
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rightNodes.push(group.nodes[i]);
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}
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queue.push(new Group(rightNodes, rightSimilaries));
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const leftNodes = [group.nodes[0]];
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/** @type {number[]} */
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const leftSimilaries = [];
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for (let i = 1; i < left; i++) {
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leftSimilaries.push(group.similarities[i - 1]);
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leftNodes.push(group.nodes[i]);
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}
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queue.push(new Group(leftNodes, leftSimilaries));
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}
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}
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}
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// lexically ordering
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result.sort((a, b) => {
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if (a.nodes[0].key < b.nodes[0].key) return -1;
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if (a.nodes[0].key > b.nodes[0].key) return 1;
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return 0;
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});
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// give every group a name
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for (let i = 0; i < result.length; i++) {
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const group = result[i];
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const first = group.nodes[0];
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const last = group.nodes[group.nodes.length - 1];
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let name = getName(first.key, last.key);
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group.key = name;
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}
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// return the results
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return result.map(group => {
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/** @type {GroupedItems} */
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return {
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key: group.key,
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items: group.nodes.map(node => node.item),
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size: group.size
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};
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});
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};
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