This repository is a compilation of useful interview questions for web developers.
Click through the link at the bottom of each problem to see the solution. All solutions are implemented in JavaScript.
To practice problems, clear the solution for the problem you want to practice, run npm run test:watch, and fill in the function to make the tests for your particular problem pass.
If I type https://google.com into my browser and press enter, what happens?
How would you go about optimizing the front-end performance of a JavaScript web application?
What is the difference between CORS and JSONP? Under what circummstances would you use each?
Define a spacify function which takes a string as an argument and returns the same string, but with each character separated by a space.
Create the same spacify function, but add it directly as a method to the String object. Talk about this practice as it relates to building real applications.
What will the result of the following be?
var User = {
count: 1,
getCount: function() {
return this.count;
}
};
console.log(User.getCount());
var func = User.getCount;
console.log(func());
How would you ensure that the context of func() is always bound to User such that 1 will be returned?
What is the complexity of a binary search? Use Big-O notation.
Implement it.
Given the following implementation of a Linked List node:
function Node(data) {
this.data = data;
this.next = null;
}
Write code to remove duplicates from an unsorted linked list given the first node in the list.
FOLLOW UP: How would you do this without access to a buffer?
Given the following implementation of a binary tree node:
function TreeNode(val) {
let node = {};
node.val = val;
node.left = node.right = null;
return node;
}
Write a function that takes the root element of the tree and inverts the tree.
Given a graph represented as an adjacency list and the node to start with, return an array of the graph's nodes in breadth first order
Given a graph represented as an adjacency list and the node to start with, return an array of the graph's nodes in depth first order
Imagine you work on a social network. People in the social network are represented as objects, where each object has the following properties:
// Person
getFriends() // returns an array of other Person objects who are direct friends with the person
getId() // returns a unique string ID representing the person
The social network wants to add a new feature inspired by "6 degrees of separation". They want to be able to tell any user how many degrees of separation they are away from someone else in the social network.
For example, A "1" means they're directly connected (that is, A is friends with B), a "2" means there is 1 mutual friend (e.g., A and B are both friends with C). A "-1" means the two friends are not connected.
Write a function that can determine the degrees of separation between two people in the social network.
Given an array of distinct integers candidates and a target integer target, return a list of all unique combinations of candidates values where the chosen values sum to target.
A candidate can be reused an unlimited number of times in a combination that sums to the target, e.g. if candidates is [2] and target is 4, [[2,2]] is an acceptable answer.
There are a total of numCourses you must take to graduate, labeled from 0 to numCourses - 1. You are given an array of prerequisites where prerequisites[i] = [a, b] indicates you must take course b first if you want to take course a.
All the pairs in prerequisites are unique.
For example, the pair [0, 1] means you need to take course 1 first before you can take course 0.
Return true if all courses can be finished. Otherwise return false.
Example 1:
Input: numCourses = 2, prerequisites = [[1, 0]]
Output: true
There are a total of 2 courses to take. Its possible to take course 0, then course 1, so it is possible to take all courses.
Example 2:
Input: numCourses = 2, prerequisites = [[1, 0], [0, 1]]
Output: false
You can't take course 1 without taking course 0, and you can't take course 0 without taking course one, so it is not possible to finish your courses.
Given a 2d array where all values are 1's (land) and 0's (water), return the number of islands;
An island is surrounded by water and is formed by connecting adjacent lands horizontally or vertically.
Assume that anything surrounding the 2d array is water.
Given an UNSORTED array of integers nums, return the length of the longest consecutive sequence of integers.
The algorith must run in O(n) time.
Example 1:
Input: nums = [100, 4, 200, 1, 3, 2]
Output: 4
Explanation: The longest consecutive sequence of integers that can be created from the list is [1, 2, 3, 4], which has a length of 4 - our answer.
Given a 2d array of letters board and a string word, return true if the word can be built from letters in the grid.
The word can be constructed from letters of sequentially adjacent cells, where adjacent cells are horizontally or vertically neighboring. The same letter cell may not be used more than once.
Example 1:
Input:
board = [
['A', 'B', 'C', 'E'],
['S', 'F', 'C', 'S'],
['A', 'D', 'E', 'E'],
];
word = 'ABCCED';
Output: true
Write a function that prints the numbers from 1 to 100.
For multiples of three print "Fizz" instead of the number.
For multiples of five print "Buzz" instead of the number.
For multiples of both three and five print "FizzBuzz".
Implement an algorithm to determine if a string has all unique characters.
Write a function to check if a string is a pallindrome.
Write a function to reverse an array.
Now do it without using any array API methods.
Now do it without a buffer.
Write a function that flattens a multi-dimensional array of unknown depth and composition into a one-dimensional array.
Pascal's triangle is a triangular array of the binomial coefficients. This means that in Pascal's triangle, each number is the sum of the two directly above it. Here's an illustration:
Write a function that prints row N of Pascal's triangle.
The Fibonacci sequence is a series of numbers where each number in the sequence is the sum of the previous two numbers. For this question, assume that the sequence starts with the number 0. The first ten numbers of the sequence look like this:
0, 1, 1, 2, 3, 5, 8, 13, 21, 34
Write two functions to compute the n'th number of the Fibonacci sequence.
The first function should use an iterative method.
The second function should use a recursive method.
Write a function that removes any duplicate characters from a string.
Write a function that finds the greatest prime factor of a number n.
The evil Professor Boolean, after years of hard work, has finally created his first successful Frankenzombie specimen. In order to understand the creature, the professor has tasked his minions with monitoring it.
Unfortunately, Professor Boolean's minions are a bit disorganized. There may be times when more than one minion is monitoring at once! Thankfully, the minions are at least organized enough to clock their hours.
Write a function that takes a list of minion timesheets [start, end] and returns the total number of hours that Frankenzombie was monitored. All values start and end are greater than zero and no greater than 2^30-1. end will always be greater than start.
Given an array of integers nums and an integer target, return indices of the two numbers such that they add up to target.
You may assume that each input would have exactly one solution, and you may not use the same element twice.
You can return the answer in any order.
Example 1:
Input: nums = [2,7,11,15], target = 9
Output: [0,1]
Explanation: Because nums[0] + nums[1] == 9, we return [0, 1].
Example 2:
Input: nums = [3,2,4], target = 6
Output: [1,2]
Example 3:
Input: nums = [3,3], target = 6
Output: [0,1]
Given a sorted integer array arr, two integers k and x, return the k closest integers to x in the array. The result should also be sorted in ascending order.
An integer a is closer to x than an integer b if:
|a - x| < |b - x|, or
|a - x| == |b - x| and a < b
Example 1:
Input: arr = [1,2,3,4,5], k = 4, x = 3
Output: [1,2,3,4]
Example 2:
Input: arr = [1,2,3,4,5], k = 4, x = -1
Output: [1,2,3,4]
Given an array of integers nums and an integer target, return the indices of the two numbers such that they add up to target.
You may assume that each input would have exactly one solution, and you may not use the same element twice.
Example 1:
Input: nums = [2, 7, 11, 15], target = 9
Output: [0, 1]
Example 2:
Input: nums = [3, 4, 2], target = 6
Output: [1, 2]
Example 3:
Input: nums = [3, 3], target = 6
Output: [0, 1]
Image that you are building Twitter. In particular, you are in charge of designing an API for Twitter's backend. This API will be used by a developer building a 3rd party Twitter client. What actions would you expose and what HTTP method would you use for each?
What are some ways you could scale your Twitter service to accomodate a high user load?
What are some ways you could scale your Twitter service to
Design a URL shortening service like bit.ly. Touch upon each of the following: - The service's database architecture - The service's API - The service's frontend web app
What is XSS and what does the acronym stand for? How is the exploit executed and what is its potential impact? How can it be mitigated?
What is SQL Injection? How is the exploit executed and what is its potential impact? How can it be mitigated?
Imagine that we have an online baking app protected by a login. Once a user has logged in, they're given a session cookie that they must have in order to send HTTP requests to the rest of the app.
For simplicity's sake, assume that the main dashboard page consists of nothing but a form that allows the user to send money to other users.
The app has two fields - a dollar amount field and a username field - and a submit button.
Submitting the form hits the following endpoint of the bank's backend API at https://www.example.com/transfer?amount=1000&destination=desiredUser, which gets the current user, queries the database to make sure the user has enough money to send the transaction, and then updates the sender's and desiredUser balances in the DB.
- What security flaw exists in this system?
- Can you elaborate on how precisely the user would exploit this flaw to steal money from a user?
- How could this flaw be mitigated?