CodeNation Interview Questions, Process, and Tips

Round duration - 90 minutes
Round difficulty - Hard

The test was from 10 pm to 11:30 pm at night, Since we had to give the test from home so it was not an uncomfortable timing for me. The test was conducted on hackerrank. Personally I find Hackerrank a better test platform than others like Amcat or Mettle.

Q1. Minimum Fountains
There is a one-dimensional garden of length 'N'. On each of the positions from 0 to 'N', there is a fountain, and this fountain’s water can reach up to a certain range as ...read more
Ans. Dynamic programming
• For every fountain, we can try to find the pair area = (left, right), where left and right are the leftmost and the rightmost index respectively where the current fountain can reach.For every index 'I' = 0 to 'I' = 'N' -1, 'LEFT' = max(0, 'I' - 'ARR'['I']) and  'right' = min('I' + ('ARR'['I'] + 1), 'N').
• Now we can sort the array of pairs in non-decreasing order according to 'LEFT' to find the mi...read more
Answered Anonymously
Add your answer
Q2. Count Inversions
For a given integer array/list 'ARR' of size 'N', find the total number of 'Inversions' that may exist.
An inversion is defined for a pair of integers in the arra...read more
Ans. Brute Force Approach
The steps are as follows:
 
1. Initialize a ‘COUNT’ with 0 to keep track of the number of inversions
2. Iterate over every element in the array in a linear fashion starting from 0.
3. For every element, check all the elements ahead of the current element and check the condition.
   1. If the condition satisfies, increase the ‘COUNT’ by 1.
   2. Otherwise, move to the next iteration.
4. Return the ‘COUNT’.
Space Complexity: O(...read more
Answered Anonymously
Add your answer
Q3. Print the array after K operations
You are given an array 'ARR' consisting of 'N' integers and a non-negative integer 'K'. Consider an operation on the array as replacing every elem...read more
Ans. Simulation, Observation.
• If ‘K’ = 0, then no operations are performed on the array. So, in this case, simply return the original array.
• We know that in each operation, we are subtracting the array elements with the maximum value in the array, so we can be sure that after one operation, we will have 0 as at least one of the elements in the array and the rest of the elements will always be +ve.
• The array values after a sing...read more
Answered Anonymously
Add your answer

Round duration - 90 minutes
Round difficulty - Hard

This interview was at 10 am in the morning and was taken by a SDE 3 of the company who had a very great background in Competitive Coding.
The interview started with me introducing myself. The interviewer then gave me a google doc which had 2 coding questions written . He asked me to go through the first question and explain the approach. After which he asked me to code the solution as well. Same procedure was followed for the second question. The most difficult part in using Google Doc to write code is that it doesn't has automatic indentation like the code editors, so I had to put much efforts in keeping my code readable.

Q1. Count distinct Bitwise OR of all subarrays
You are given an array consisting of N positive integers, your task is to count the number of distinct possible values that can be obtained by taking the bitwise ...read more
Ans. 
I had read this article few days before the interview so I was aware of the approach that was efficient. But I started by explaining the naive O(N^3) solution.
The interviewer asked me to optimize the approach.
Then I gave him the approach I read in the article.
The interviewer asked me to code the solution which I did.
Answered Anonymously
Add your answer
Q2. Colour the Graph
You are given a graph with 'N' vertices numbered from '1' to 'N' and 'M' edges. You have to colour this graph in two different colours, say blue and red suc...read more
Ans. DFS
We can approach this problem by running a DFS starting from vertex-1.
We have a total of ‘m’ edges.
When can we achieve the configuration when we see in reference to vertex-1? 
1. Let's say vertex-1 is ‘Blue’
   1. If all the vertices that connect to vertex-1 are ‘Red’, then we can say that the configuration is possible.
2. If this would be the negation of the last one. Say, vertex-1 is ‘Red’
   1. If all the vertices that connect to ...read more
Answered Anonymously
Add your answer

Round duration - 60 minutes
Round difficulty - Hard

The round was at 4 pm evening. This round was taken by one of the Vice President of the company, this made me anxious from the very beginning.
The interviewer was a knowledgeable man and had great knowledge in every field. He always demanded exact answers.
The round started with my resume walk through. Then came open ended questions followed by a system design question in which I failed miserably.

Round duration - 45 Minutes
Round difficulty - Medium

This was a straight coding round with three questions , I was able to solve all 3

Q1. Kth Largest Number
You will be given a stream of numbers, and you need to find the kth largest number in the stream at any given time.
As the stream of numbers can not be given during compile time, so yo...read more
Ans. Brute Force
• The brute force approach for this problem is very trivial.
• We can always maintain an array that will hold the integers, sort the array in non-increasing order and return the element present at the kth index(1-based indexing).
• The array should be such that it can add elements efficiently, for example, vectors in C++, lists in python, etc. Whenever we receive a query of type 1, we add the element in the array an...read more
Answered Anonymously
Add your answer
Q2. Rat In A Maze
You are given a starting position for a rat which is stuck in a maze at an initial point (0, 0) (the maze can be thought of as a 2-dimensional plane). The maze would be given in the form of a...read more
Ans. Bactracking
Approach: We can start the traversal of the paths from the rat’s starting position, i.e. (0,0) keeping track of the visited cells during the traversal. We will recursively go through all the paths possible until the last index of the grid (destination) is reached, and add the path information using which the rat successfully reached the end.
 
Algorithm is as follows:
 
1. Take the starting position of th...read more
Answered Anonymously
Add your answer

Round duration - 60 Minutes
Round difficulty - Medium

As this was my first system design round, I was not expecting to be able to tell anything , but to my surprize he interested in just the idea what I can think , how I can solve some issues which need not be definitely to have a solution / or multiple solutions are possible from common sense.

I was given an Idea based question