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 Activation Problem
In this problem, you have a one-dimensional garden of length 'N'. Each position from 0 to 'N' has a fountain that can provide water to the garden up to a certain range...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
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Q2. 
Count Inversions Problem Statement
Given an integer array ARR of size N, your task is to find the total number of inversions that exist in the array.
An inversion is defined for a pair of integers in the...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
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Q3. 
Array Transformation Problem
Given an array ARR consisting of N integers and a non-negative integer K. An operation on the array replaces each element ELE with MX - ELE, where MX is the maximum element of...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
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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
Given an array of positive integers, determine the number of distinct values obtained by applying the bitwise OR operation on all possible subarrays.
Explanatio...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.
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Q2. 
Graph Coloring Problem
You are given a graph with 'N' vertices numbered from '1' to 'N' and 'M' edges. Your task is to color this graph using two colors, such as blue and red, in a way that no two adjacen...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
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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 Problem Statement
You are given a continuous stream of numbers, and the task is to determine the kth largest number at any moment during the stream.
Explanation:
A specialized data st...read more
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Q2. 
Rat in a Maze Problem Statement
You need to determine all possible paths for a rat starting at position (0, 0) in a square maze to reach its destination at (N-1, N-1). The maze is represented as an N*N ma...read more
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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