Master the JavaScript interview with expertly curated questions and solutions. Strategies developed by FAANG engineers help you prep faster, boost confidence, and refine your problem-solving skills.

Master the JavaScript interview by practicing 20 carefully curated interview questions and solutions. These problems will provide the tools you need to tackle any question you find in an interview. Allow ~1 hour per question.

Most questions have multiple solutions presented. All solutions are thoroughly explained and time and space complexity are discussed. A passing familiarity with these ideas is expected. You'll learn how to tackle different types of problems so you can proceed with confidence in your interviews.

These questions go beyond the common problems that we've all seen. FizzBuzz and bubble sort? We start past those.

We'll discuss how to refine algorithms. We'll go over clever, advanced ways of manipulating data that interviewers are looking for. You'll walk away more skilled and confident in your problem solving and interviewing abilities.

This course is taught in ES2015.

Master the JavaScript Interview

# Remove Dupes

## Instructions

Write a function that takes in a string and returns a new string. The new string should be the same as the original with every duplicate character removed.

**Input**: String

**Output**: String

## Examples

    'abcd' -> 'abcd'
    'aabbccdd' -> 'abcd'
    'abcddbca' -> 'abcd'
    'abababcdcdcd' -> 'abcd'

---

function removeDupes(str) {
    // Your code here
}

# How it Works

We create an object and an array, both of which will hold unique characters.

The for-loop goes through every character and checks if it's present in our object. If so, do nothing. It's a duplicate letter.

If not present in our object, we need to insert it into both the object and the array.

We need to maintain both the object and the array because they perform different functions for us. The object will allow us to check if we've already seen the letter instantaneously. However, objects don't keep track of the order that items are inserted in. For that, we also need to push the characters into an array.

At the end, we join all the characters in the array together and return the string.

## Time

We have to process every character, so our time complexity is:

### O(n)

## Space

We store every character twice, in an array and in an object. This gives us `O(2n)` which simplifies to:

### O(n).

---

As mentioned in *"Is Unique"*,  JavaScript received a new data structure that allows items to be inserted only once *and* keeps track of insertion order. Using this construct, the `Set`, we can greatly simplify our code.

In this lesson, we'll discuss how to remove duplicates from a string. We'll cover two different solutions and see how ES2015 constructs can greatly simplify our code.

Introduction

Strings & Arrays

Advanced Strings & Arrays

Algorithms & Data Structures

JavaScript Mastery

Conclusion

Remove Dupes

Remove Dupes

Instructions