Oyo Rooms Software Developer Intern Interview Questions, Process, and Tips

Round duration - 90 minutes
Round difficulty - Hard

Timing was 11 am. Platform was quite well.

Q1. 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 by CodingNinjas
Add your answer
Q2. Minimum Cost to Destination
You have been given an N*M matrix where there are 'N' rows and 'M' columns filled with '0s' and '1s'.


'1' means you can use the cell,...read more
Ans. Backtracking
Maintain a visited array and try to explore all the possibilities with the help of backtracking.
1. Start with (0, 0) and mark it as visited and try to move in all 4 directions.
2. Say at any point we are at (i, j) then the cost of reaching (x,y) will be the minimum of these four cases.
   1. Option 1 -  Left: cost of reaching from (i, j-1)
   2. Option 2 - Right: cost of reaching from (i, j+1)
   3. Option 3 - Up: 1 + cost of rea...read more
Answered by CodingNinjas
View 2 more answers

Round duration - 90 minutes
Round difficulty - Easy

Q1. Detect Cycle in a Directed Graph
Given a directed graph, check whether the graph contains a cycle or not. Your function should return true if the given graph contains at least one cycle, else return false.
...read more
Ans. 
I used DFS from every unvisited node. There is a cycle in a graph only if there is a back edge present in the graph.
To find the back edge to any of its ancestor keep a visited array and if there is a back edge to any visited node then there is a loop and return true.
Answered by CodingNinjas
View 1 more answer
Q2.  Next Permutation
You have been given a permutation of ‘N’ integers. A sequence of ‘N’ integers is called a permutation if it contains all integers from 1 to ‘N’ exactly once. Your task is to rearrange the...read more
Ans. 
Traverse from right and find the first item that is not following the descending order.
Swap the found character with closest greater (or smallest greater) element on right side of it.
After swapping, sort the string after the position of character found.
Answered by CodingNinjas
View 2 more answers

Round duration - 60 minutes
Round difficulty - Easy

Q1. Validate BST
Given a binary tree with N number of nodes, check if that input tree is BST (Binary Search Tree) or not. If yes, return true, return false otherwise.
A binary search tree (BST) is a binary t...read more
Ans. 
I gave him two three approaches.
Brute force
using utility class
using in-order traversal:
Answered by CodingNinjas
View 2 more answers

Round duration - 90 minutes
Round difficulty - Medium

The test was scheduled at 2:30 PM, IST. The test was conducted online, due to the ongoing pandemic situation. Webcam was required to be switched on during the complete duration of the test. I had solved 2/2 coding questions with all test cases successfully passing. Out of the 10 MCQ questions, I had done 6. Around 90 students sat for the online coding round, 19 were shortlisted for the interview. Those who had solved both coding questions were called for interview.

Q1. Candies
Prateek is a kindergarten teacher. He wants to give some candies to the children in his class. All the children stand in a line and each of them has a grade according to his or her performance in ...read more
Ans. 
Step 1: Since we had to see adjacent students' marks, and then decide the candy to be given, dynamic programming struck my mind.
Step 2: We need to look in both sides, left as well as right. So I constructed an array, say left, in the first traversal.

 
Answered by CodingNinjas
View 2 more answers
Q2. Min cost to reach N
Ninja Yuki is in the mood of shopping ninja blades today, and why should he not be, its finally the time for the Spring Fair in his Village. Initially, he has 0 number of blades and aim...read more
Ans. 
This was a simple DP based problem. Construct a DP array of size n+1. And fill the array as follows:
For i between 2 to n:
1). If i is even: then we can reach that i by two ways, one is by adding 1 to i-1, another by doubling i/2, and add their respective costs.
Therefore, dp[i] = min(dp[i-] + A, dp[i/2] + B);
2). If i is odd. This is a bit tricky, one option is adding one to i-1. Since this is not an even no. so we cant d...read more
Answered by CodingNinjas
View 3 more answers

Round duration - 60 minutes
Round difficulty - Medium

This was a pure DSA based round. Two questions were asked in this round. The interviewer was quite good, and helped in between.

Q1. First Unique Character in a String
You are given a string A consisting of lower case English letters. You have to find the first non-repeating character from each stream of characters.
For Example: If th...read more
Ans. 
I had solved this question earlier, thanks to Coding Ninja's Codezen. I was able to give the optimised solution. I used the concept of deque. The question was based on the concept of sliding window.
Answered by CodingNinjas
View 3 more answers
Q2. Boolean Matrix
Given a 2-dimensional boolean matrix mat of size N x M, modify the matrix such that if an element is 1, set its entire row and column to 1 i.e. if mat[i][j] = 1, then make all the elements o...read more
Ans. 
I started with the naive approach. I suggested storing the location of all 1s in an array. Then traverse over this array and make required changes in the matrix.
The interviewer asked me to optimise it further. I suggested, when we encounter a one, start making changes in the matrix as: if m[i][j] is 0 then change it to 1, else change the value to -1, so that we know a 1 was present here and change its respective column...read more
Answered by CodingNinjas
View 2 more answers

Round duration - 75 minutes
Round difficulty - Medium

This round was also again focused on DSA. Two interviewers were present. This round was very extensive and everything was asked in depth as well as they asked to write the codes as well for all the questions. I was also asked to explain my projects, they were based on ML. Many aspects of OOPs, POP, memory allocation was asked as well.

Q1. Maximum sum of (i*Arr[i]) among all possible rotations of an array.
You are given an array 'ARR' consisting of 'N' elements, and you need to find the maximum value of sum(i * ARR[i]) among ...read more
Ans. 
first found the value of f(0). Now what we need to do is assign last element the index 0, then in next iteration, the 2nd last element as index 0 and last as index 1.
So i ran a loop from 1 to n, and i in each iteration, the last i elements were assigned indices starting from 0. After that, continuing from the last index that was assigned to the last element, we start picking elements from the start.
Sum these values and
Answered by CodingNinjas
View 2 more answers
Q2. Averages of Levels in Binary Tree
You are given an arbitrary binary tree consisting of 'N' nodes numbered from 1 to 'N', and each node is associated with some positive integer value. Your ...read more
Ans. 
This was a simple BFS traversal problem. I was also asked to write the code for the same. I was able to code it successfully.
Answered by CodingNinjas
View 1 more answer

Round duration - 60 minutes
Round difficulty - Medium

Q1. Longest Increasing Subsequence
For a given array with N elements, you need to find the length of the longest subsequence from the array such that all the elements of the subsequence are sorted in strictly ...read more
Ans. Recursive Approach
• We will write a recursive algorithm that will try all the possibilities.
• The argument of recursive function will be the current index and what was the previous number used for LIS. Initially, we will be passing the previous number as the minimum number of an integer and starting index as 0.
• The base case would be when we reach index n,i.e we have exhausted the array elements so return 0 because there is...read more
Answered by CodingNinjas
View 4 more answers
Q2. Digits Decoding
A few days back, Ninja encountered a string containing characters from ‘A’ to ‘Z’ which indicated a secret message. For security purposes he encoded each character of the string to its nume...read more
Ans. Recursion
• The idea is to use recursion to reduce the big problem into several small subproblems.
• We will call a helper function that returns us the number of valid de-codings.
  The helper function works in a way that initially, we will pass the sequence of length n to it. 
  Further, we will calculate the possible answer for the subsequence of length n-1 recursively. 
  Similarly, if it's valid, we will calculate the ...read more
Answered by CodingNinjas
View 4 more answers

Round duration - 60 minutes
Round difficulty - Medium

Q1. Leaves at same level
Bob has been given a binary tree having N nodes. He has been asked to check if all the leaf nodes are at the same level.
Your task is to help Bob in checking if all the leaf nodes a...read more
Ans. 
I gave a level-order traversal solution using queue and then he asked me to optimise it to O(1) space.
Answered by CodingNinjas
View 1 more answer
Q2. Maximum sum of non-adjacent elements
You are given an array/list of ‘N’ integers. You are supposed to return the maximum sum of the subsequence with the constraint that no two elements are adjacent in the ...read more
Ans. 
Gave him a recursive solution then optimised it using DP(to O(n) time and O(n) space) and then again optimised to O(1) space.
Answered by CodingNinjas
View 3 more answers

Round duration - 60 minutes
Round difficulty - Medium

Q1. LRU Cache Implementation
Design and implement a data structure for Least Recently Used (LRU) cache to support the foll...read more
Ans. 
Code this problem beforehand. It's a very common problem.
Answered by CodingNinjas
View 2 more answers
Q2. Doors Puzzle
There are 100 doors in a row, all doors are initially closed. A person walks through all doors multiple times and toggle (if open then close, if close then open) them in following way: 
In...read more
Add your answer
Q3. Operating System
Tell the difference between Mutex and semaphores.
Add your answer
Q4. DBMS
What is Indexing, why it is done and explain all the types of Indexing?
Add your answer
Q5. DBMS
Given employee and dept table find the no of employees in each dept(Question on Joins).
Add your answer
Q6. OOPS Questions
Difference between function overloading and function overriding with example. And also about runtime and compile time binding while overriding.
Add your answer