Skip to main content

Coding Interview Questions Set 1

From this article, I will be sharing with you all a series of articles on coding interview questions.
So please stay connected for the latest set of questions.
It will be a good brainstorming exercise and will also prepare
you for coding interviews and will definitely boost your confidence.

So let's start,

1)Reverse of a string with only O(1) extra memory.


var reverse = function(string) {
    let result = ''
    for(let i= string.length -1; i >= 0; i--){
        result += string[i];
    return result;

2)Fizz Buzz: Write a program that will accept a number n and will output number till n but for multiples of three it should output “Fizz” instead of the number and for the multiples of five output “Buzz”. For numbers which are multiples of both three and five output “FizzBuzz”.


var fizzBuzz= function(n) {
    const arr=[]
    for(i=1; i<=n; i++){
        if(i%15===0) arr.push("FizzBuzz")
        else if(i%3===0) arr.push("Fizz")
        else if(i%5===0) arr.push("Buzz")
        else arr.push(i.toString())
    return arr

3)Find a single element in an array of multiple elements where every element appears twice except the one you have to find. Do it in O(n) and with no extra memory.

There are multiple solutions that you can solve this in javascript,


function findSingle(nums) {
 return nums.reduce((prev, curr) => prev ^ curr, 0);

The reduce method in JS reduces the array to a single value.
XOR will return 1 only on two different bits.
So if two numbers are the same, XOR will return 0.
Finally, only one number left.
A ^ A = 0 and A ^ B ^ A = B.

b)You have to find it out and have to post it in the comments section.
Hope to see someone in the comment section.

I hope you like this article.
Please stay connected for coding interview questions set 2.
Don't forget to subscribe to this blog.
You can also follow me on Twitter or Linkedin for the latest updates.

Written By:

Saurabh Joshi


  1. const findSingle = (arr) =>
    arr.reduce((acc, curr, idx) => {
    if (acc.includes(curr)) {
    acc.splice(acc.indexOf(curr), 1);
    return acc;
    else { return acc.concat([curr])}
    }, [])

  2. Your solution for (1) creates O(n) extra memory. For O(1), you need to reverse the input string in-place, with a fixed-size variable to facilitate 3-line-swaps:

    var reverse = function(str) {

    var tmp = '';
    str = str.split('');

    for(let i = 0; i < str.length / 2; i++) {
    tmp = str[i];
    str[i] = str[str.length - 1 - i];
    str[str.length - 1 - i] = tmp;

    return str.join('');

    1. You allocate a new array in "result" instead of reversing in-place.

      For input array length n, you allocate n more bytes to hold result.
      For input length 2*n, allocate 2*n extra,
      For input length 3*n, allocate 3*n extra.

      Extra memory graph will look like f(x) = x

      My method always allocates the same extra memory ("tmp"), no matter how input length increases. So the graph will look like f(x) = 1 or some constant. Flat horizontal graph.

      Consider this similar problem, it also works in-place:

    2. Result is not an array it a string varia lble. And I am just appending it .

    3. How much memory does your "result" allocate when input "string" is length 100? 200? 300?

  3. Replies
    1. I am glad. Thank you for these posts. May your life be full of teachers.


Post a Comment

Popular posts from this blog

Node JS:Understanding bin in package.json.

Well as a Node Js developer we know package.json as dependency file where we keep a note of all dependencies of our project. Here we will be looking at what is bin in package.json? To understand this we first need to understand command line application and it's purpose. CLI applications are mostly used to automate things such as deployments of application,running tests,building reports and the list goes on and on. So lets start with creating our first CLI application. First, let’s make sure you have the tools required. To complete this tutorial, you will need the following: 1)A recent version of Node.js downloaded and installed 2)A good text editor, such as Visual Studio Code Next, open your computer’s command prompt (Windows) or terminal (macOS/Linux). Change the current directory to the folder where you save your documents or projects. Enter the following commands to create a new project folder and initialize the project. mkdir hello-cli cd hello-cli npm init Nex

Node.js: Extract text from image using Tesseract.

In this article, we will see how to extract text from images using Tesseract . So let's start with this use-case, Suppose you have 300 screenshot images in your mobile which has an email attribute that you need for some reason like growing your network or for email marketing. To get an email from all these images manually into CSV or excel will take a lot of time. So now we will check how to automate this thing. First, you need to install Tesseract OCR( An optical character recognition engine ) pre-built binary package for a particular OS. I have tested it for Windows 10. For Windows 10, you can install  it from here. For other OS you make check  this link. So once you install Tesseract from windows setup, you also need to set path variable probably, 'C:\Program Files\Tesseract-OCR' to access it from any location. Then you need to install textract library from npm. To read the path of these 300 images we can select all images and can rename it to som

Node.js: Bundling your Node.js application to single executable for Windows.

In this article, we will see how to bundle Node.js application to a single executable for Windows. What's the need? Well recently, I had taken a work where I needed to convert pdf's(Of similar format) to excel sheet. So I was reading the pdf's from a folder in desktop and I was storing the output excel sheet into a separate folder on the desktop. I used Node.js for the program. Now the client wanted it to install the program on 25 windows machine and his budget was really low. So it was also not possible for me to install node.js for 25 machines and then install the required dependency for each one. One of the solution: While I was searching for an easy solution I found this amazing npm module pkg . This module can make your node.js app work like plug and play type. No need to install Node.js on the client machine or any other dependency.  It helps to make a commercial or trial version of your node.js application without exposing the source code. I found