JavaScript Algorithm

1.js

// Find missing numbers in the array

const numbers = [1, 2, 7, 3, 5, 4, 9]
let missing = []

for (var i = 1; i <= Math.max(...numbers); i++) {
  if (!numbers.includes(i)) {
    missing.push(i)
  }
}

console.log(missing) // [6, 8]

2.js

// Find min and/or max number in the array

const numbers = [-10, 7, 29, 30, 5, -10, -70]

console.log(findMinMax(numbers)) // { min: -70, max: 30 }

function findMinMax (array) {
  return {
    min: Math.min(...array),
    max: Math.max(...array)
  }
}

3.js

// Remove duplicate entries from the array

const entries = [1, 2, 3, 5, 1, 5, 9, 1, 2, 8]

console.log(uniqueEntries(entries)) // [1, 2, 3, 5, 9, 8]

function uniqueEntries (array) {
  return Array.from(new Set(array))
}

4.js

// Find vowels in the string

const testString = 'Hello World'

console.log(findVowels(testString)) // ["e", "o", "o"]

function findVowels (string) {
  return string.match(/[aeiou]/gi)
}

5.js

// Array chunking
const array = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15]

console.log(chunkArray(array, 3))

function chunkArray (array, size) {
  let output = []
  let index = 0

  while (index < array.length) {
    output.push(array.slice(index, index + size))
    index += size
  }

  return output
}

6.js

// Find character repeated most of the time

const sample = 'Hi there, this is just a sample!'

console.log(
  getMostRepeatedCharacter(
    countRepeatedCharacters(sample)
  )
) // { count: 4, character: "s" }

function countRepeatedCharacters (string) {
  const characters = string.replace(/\s+/g, '').split('')
  let output = {}

  characters.forEach(character => {
    output[character] = output[character] + 1 || 1 // increment by one or start with one
  })

  return output
}

function getMostRepeatedCharacter (object) {
  let output = { count: 0, character: null }
  
  Object.keys(object).forEach(key => {
    if (object[key] > output.count) {
      output.count = object[key]
      output.character = key
    }
  })
  
  return output
}