Solving common algorithmic questions in JavaScript

Have you ever tried to develop an algorithm for solving a problem in a technical interview? In this short tutorial, we'll tackle three main questions about algorithm design, starting with brute force (step by step, but not necessarily efficiently) and moving on to a more streamlined, elegant solution.

Line spread

Task

Having received the string, you need to expand it.

Solution # 1

string.substring(), str . .

— , . , myString.substring(1), .

() . . , .

, , string.charAt(). charAt : , .

.

//  №1: Substring
function reverseString(str) {
    let reversedString = '';

   /*       str
  ,    i  str.length
      str,   ,   .
   */
    for (let i = str.length; i > 0; i--) {
        reversedString += str.substring(i, i-1);
    }
    return reversedString;
}

//  №2: CharAt
function reverseString(str) {
    let reversedString = '';

   /*        str
      i  str.length-1   ,  i    0.

  ,   ,   
   */
    for (let i = str.length-1; i >= 0; i--) {
        reversedString += str.charAt(i);

    }
    return reversedString;
}

№2

— , .

:

string.split() — .

string.reverse() — .

string.join() — .

.

function reverseString(str) {
  return str.split('').reverse().join('');
}

.

№1

string.split(' ') . , .

. . , , ! , .

for array.forEach(). , , .

//     for
function findLongestWordLength(str) {
  let maxVal = 0;

  const wordArr = str.split(' ');

  for(let i = 0; i < wordArr.length; i++) {
      let word = wordArr[i];
      if (word.length > maxVal) {
          maxVal = word.length;
      }
  }
  return maxVal;
}

//     array.forEach
function findLongestWordLength(str) {
  let maxVal = 0;

  const wordArr = str.split(' ');

  wordArr.forEach(word => {
      if (word.length > maxVal) {
          maxVal = word.length;
      }
  });
  return maxVal;
}

№2

, string.split(), .

array.map(), . , .

arrOfLengths.

, Math.max(...spreadOperator) spread , .

function findLongestWordLength(str) {
  const arrOfWords = str.split(' ');
  const arrOfLengths = arrOfWords.map(item => item.length);

  return Math.max(...arrOfLengths);
}

, . 4 .

[1,2,3,4]
[5,18,0,12]
[3,5,12,5]
[28,9,2,34]

Should return => [4,18,12,34]

№1

for-loop.

, .

//    for
function largestOfFour(arr) {
  let arrayOfMaxValues = [];
  for (let i = 0; i < arr.length; i++) {
      let subArr = arr[i];
      let maxSubArrVal = 0;
      for (let j = 0; j < subArr.length; j++) {
          let currentValue = subArr[j];
          if (currentValue > maxSubArrVal) {
            maxSubArrVal = currentValue;
          }
      }
      arrayOfMaxValues.push(maxSubArrVal);
  }
  return  arrayOfMaxValues;
}

//   forEach
function largestOfFour(arr) {
  let arrayOfMaxValues = [];
  arr.forEach(subArr => {
     let maxSubArrVal = 0;
     subArr.forEach(item => {
        if (item > maxSubArrVal) {
            maxSubArrVal = item;
        }
     });
     arrayOfMaxValues.push(maxSubArrVal);
  });
  return  arrayOfMaxValues;
}

№2

Math.max(...spreadOperator) array.map() , .

function largestOfFour(arr) {
  return arr.map(subArr => Math.max(...subArr));
}

"Breaking Down JavaScript Solutions To Common Algorithmic Questions (Part 1)" by Emma Bostian

. , — !

I broadcast this and many other useful articles for beginner Frontend developers on the Frontend.school () Telegram channel , where I also prepare useful quizzes to test my knowledge. I draw your attention to the fact that the channel is purely a hobby and a desire to help and does not bring material benefits for me.