There were 3 technical rounds. First was a Codility coding test. You can take it anytime within 7 days. Second was a pair coding interview which involved live coding in front of 2 interviewers. Both interviewers were backend engineers but not seniors.

Third was a design interview, where you have to draw a design on an online platform called Figma. In this one, your interviewers will be seniors.

(1) Codity questions (3 coding problems described below) :

(1) You are given implementation of a function. This function, given a non-empty array A of N integers (sorted in non-decreasing order) and integer K, checks whether A contains numbers 1,2, ..., K (every number from 1 to K at least once) and no other numbers. The goal of the exercise is to find and fix bug(s) in the implementation.

(2) In 1 step, any element of a given array can be either increased or decreased by 1. Write a function that, given an array A of N integers, returns the minimum number of steps required to make all elements equal.

(3) There are N arrows. The K-th arrow is rotated clockwise by A[K] degrees from an upward direction. In 1 move you can rotate 1 arrow clockwise or counter-clockwise by an arbitrary angle. What is the minimum sum of rotation angles needed to make all arrows point in the same direction. Write a function that, given an array A made of N integers, describing the initial rotation of each arrow, returns the minimum sum of rotation angles needed to make all arrows point in the same direction.

(2) Coding interview:

(1) Code LeetCode easy level question. (3 Sum).

(2) If a client sends invalid or unexpected input to a REST API, what should the API ideally return?

(3) What are sealed interfaces? When / why do we use it?

(4) If a REST API needs to return null to the client, should it return a simple null or return an object of type Optional ? When to use Optional? What are the benefits of using Optional? If the type of input from the client is not as expected, would you prefer to return a null, or an error message or an empty collection?

(5) If a variable is of type Optional, do we still need to perform a null check before calling methods on it? What happens if we don't? Error or warning?

(3) Design interview

(1) Design a new user registration system, including the email verification/confirmation flow.