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// similar to map, but works with nested arrays
const deepMap = (arr, fn, idxs = [], startLen = 0) => {
  const res = [];
	for (let i = 0; i < arr.length; ++i) {
    const len = startLen + res.length;
    if (Array.isArray(arr[i])) {
      res.push(...deepMap(arr[i], fn, [...idxs, i], len));
    } else {
      res.push(fn(arr[i], idxs, len));

gkucmierz

const KMPSearch = (() => {
  const computeLPSArray = pat => {
    let len = 0;
    let i = 1;
    const lps = [0];
    while (i < pat.length) {
      if (pat[i] === pat[len]) {
        ++len;
        lps[i] = len;

gkucmierz

// play sine wave in browser

const sound = (() => {
  return {
    play: (duration = 1e3) => {
      const context = new AudioContext();
      const o = context.createOscillator();
      o.type = 'sine';
      o.connect(context.destination);
      o.start();

gkucmierz

// union find
// quick-union with path compression

const unionFind = n => {
  const arr = new Uint32Array(n);
  for (let i = 0; i < n; ++i) {
    arr[i] = i;
  }
  
  const root = p => {

gkucmierz

// sort first array using another array
// - both arrays are same length
// - sort is stable

function sortUsing(a1, a2) {
  const a = [];
  for (let i = 0; i < a1.length; ++i) {
    a[i] = [a1[i], a2[i], i];
  }
  return a.sort((a, b) => {

gkucmierz

const print2dGrid = (grid, pad = 2) => {
  const p = ' '.repeat(pad);
  console.log(['', ...grid.map(r => r.map(n => (p+n).substr(-pad)).join` `), ''].join`\n`);
};

const square = [
    [1, 2, 3, 6, 2, 8, 1],
    [4, 8, 2, 4, 3, 1, 9],
    [1, 5, 3, 7, 9, 3, 1],

gkucmierz

// select data based on ranges description
// min and max are optional
// ranges are testet from bottom to top and vice versa

const conditionalRange = (n, ranges, def) => {
  for (let i = 0; i < ranges.length; ++i) {
    const r = ranges[i];
    if ('max' in r) {
      if ('min' in r) {
        if (r.min <= n && n <= r.max) return r.data;

gkucmierz

// big int
const BigInt = function BigInt(n = '0') {
  const str = (n.join && n.join`` || n + '').replace(/^0+/, '') || '0';
  const sign = str[0] === '-' && +n !== 0;
  const arr = [...str.replace(/^\-/, '')].map(n => +n);
  
  const calcDbl = bi => {
    return [1, 2, 3].reduce(([dbl, acc]) => {
      acc = acc.add(acc);

gkucmierz

// array intersection that correctly handles also duplicates

const intersection = (a1, a2) => {
  const cnt = new Map();
  a2.map(el => cnt.set(el, cnt.has(el) ? cnt.get(el) + 1 : 1));
  return a1.filter(el => cnt.has(el)).filter(el => {
    const left = cnt.get(el);
    if (0 < left) {
      cnt.set(el, left - 1);
      return true;

gkucmierz

function groupBy(arr, fn) {
  fn = fn || ((o) => o);
  let g = [];
  let v = [];
  for (let i = 0; i < arr.length; ++i) {
    let val = fn(arr[i]);
    let idx = g.indexOf(val);
    if (idx === -1) {
      g.push(val);