okovalov

const twoSum = (arr, num) => {
  const result = []
  const hash = []

  for (let i in arr) {
    const currentNumber = arr[i] 
    const expectedNumber = num - currentNumber 
    
    if (hash.indexOf(expectedNumber) !== -1) {
      result.push([currentNumber, expectedNumber])

okovalov

/**
 * An idea how to address this 'issue'
 * js> 0.1+0.2==0.3
 *  false
 * 
 * The problem here is that number does not always equal to what is displayed
 * js> (0.1).toPrecision(21)
 * 0.100000000000000005551
 * js> (0.2).toPrecision(21)
 * 0.200000000000000011102

okovalov

/**
 * A random integer between given min and max
 */
const getRandomNumber = (min = 1, max = 10) => Math.floor(Math.random() * (max - min + 1)) + min

const min = 10
const max = 15

for (let i = 1; i <= 10; i++) {
  console.log(`Random number between ${min} and ${max} = ${getRandomNumber(min, max)}`)

okovalov

/**
 * Fibonacci
 * 
 * 1, 1, 2, 3, 5, 8, 13, 21, 34
 * 
 * fibonacci = O(n^2) - exponential
 * fibMemo = O(n) - linear
 */

/** O(n^2) **/

okovalov

const binarySearch = (arr, key) => {
  const midIdx = Math.floor(arr.length / 2)
  const midElement = arr[midIdx]

  if (midElement === key) return true
  if (arr.length === 1) return false
  
  if (midElement > key) {
    return binarySearch(arr.splice(0, midIdx), key)
  }

okovalov

const sieveOfErathosphenes = num => {
  const arr = [false, false]

  for (let idx = 2; idx < num; idx ++) {
    arr[idx] = true
  }

  for (let i = 2; i <  Math.sqrt(num); i++) {
    for (let j = 2; j * i <= num; j++) {
      arr[i * j] = false

okovalov

const bubbleSort = arr => {
  const { length } = arr
  
  for (let i = 0 ; i < length; i++) {
    for (let j = 0; j < length - i - 1; j++) {
      if (arr[j] > arr[j+1]) {
        const temp = arr[j]
        arr[j] = arr[j + 1]
        arr[j+1] = temp
      }

okovalov

const mergeSort = arr => {
  if (arr.length < 2) return arr
  const middleIdx = Math.floor(arr.length / 2)

  let left = arr.splice(0, middleIdx)
  let right = arr.splice(0)

  return merge(mergeSort(left), mergeSort(right))
}

okovalov

/**
 * n = 20
 * 
 * test merge: 0.517ms
 * test bubble: 0.204ms
 * 
 * n = 100
 * 
 * test merge: 3.295ms
 * test bubble: 1.395ms

okovalov

const maxProfit = arr => {
  let bestBuyPrice = 1000000
  let maxProfit = -1

  for(let i = 0; i < arr.length - 1; i++) {
    const currentBuyPrice = arr[i]
    const nextSellPrice = arr[i+1]

    if (currentBuyPrice < bestBuyPrice) bestBuyPrice = currentBuyPrice