okovalov

/**

Find the minimum value in an array of strings using a loop. For example, for this array:
  a=['my','name','is','john','doe'];
  
**/

const sortByLengthOnly = arr => arr.sort( (a, b) => a.length - b.length)

const sortByLengthAndValue = arr => arr.sort( (a, b) => { 

okovalov

-- 
-- There is a `t` table with 3 fields:
--   `uid` - user ID
--   `dt` - date and time of message
--   `s` - text of the message
--   Write an SQL query to retrieve date and text of the last message for all users.
  
-- schema
CREATE TABLE `user_message_log` (
  `id` int(11) NOT NULL AUTO_INCREMENT,

okovalov

{
  "env": {
    "browser": true,
    "node": true,
    "es6": true
  },

  "plugins": ["react"],

  "ecmaFeatures": {

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 

okovalov

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

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

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 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 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

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

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