Zomato Software Developer Intern Interview Questions, Process, and Tips

Round duration - 150 minutes
Round difficulty - Medium

The interview was scheduled at 6 pm and the duration of the interview was 1.5 hrs but went for around 2.5 hrs. The interviewer started with a brief intro about me. Asked me some coding questions. After coding questions he started asking questions on dbms like difference between sql and no sql, what is horizontal and vertical scaling and when we use them. Then some questions on computer networks like how web browsers works, different between http and HTTPS, what is TCP. After this he asked about my projects and the technology I worked on during the intern.

Q1. 
Snake and Ladder Problem Statement
Given a Snake and Ladder Board with 'N' rows and 'N' columns filled with numbers from 1 to N*N starting from the bottom left of the board, and alternating direction each...read more
Ans. BFS
We will use Breadth-First Search to find the shortest path from cellNumber 1 to cellNumber N*N.
1. We will maintain a queue of cellNumber where the front of the queue will always contain a cell which can be reached by minimum dice throw from starting cell (cellNumber = 1).
2. Create a minDiceThrow array of size N*N initialise it with the maximum value (INT_MAX)
3. Start with pushing cellNumber 1 and updating minDiceThrow[1] = 0...read more
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Q2. 
Deletion In Doubly Linked List
You are given a Doubly Linked List with 'N' positive integers. Your task is to delete a node at a given position 'POS' in this linked list.
Input:
The first line of input ...read more
Ans. Naive Approach
If ‘POS’ is 0 means that we have to delete a node at the beginning of the linked list means we have to make the 2nd node as the head node so just set ‘head’  = ‘head → next’ and ‘head → prev’ = ‘NULL’. 
 
If ‘POS’ is ‘N - 1’ means that we have to add a node at the end of the linked list so just traverse to position ‘N - 2’ of the linked list and set the ‘NEXT’ of the node as ‘NULL’.
 
If ‘...read more
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Round duration - 20 minutes
Round difficulty - Easy

Round duration - 90 minutes
Round difficulty - Medium

The interview started in the evening on google meet. and extended for 90 minutes. The interviewer was very helpful and he shared a collaborative code editor to discuss several problems.

Q1. 
Find All Pairs Adding Up to Target
Given an array of integers ARR of length N and an integer Target, your task is to return all pairs of elements such that they add up to the Target.
Input:
The first line ...read more
Ans. 
Step 1 : I first explained an iterative approach for the problem. The solution had O(N) complexity.
Step 2 : Interviewer asked me to optimise the solution.
Step 3 : Then I gave a solution that involved using binary search as the array was already in sorted order that reduced the solution complexity to O(log N) and the interviewer was happy.
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Q2. 
Convert a Binary Tree to a Sum Tree
Given a binary tree of integers, convert the binary tree into a sum tree where each node's value is replaced by the sum of the values of its left and right subtrees in ...read more
Ans. 
Step 1 : I explained a solution that involves calling nodes reclusively and calculating the sum of all children and adding them together to check the condition. After calculating I returned sum of children with the node value from the function. 

The solution has time complexity of O(N) when N is number of nodes and the interviewer was happy with my approach.
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Q3. 
LFU Cache Design Problem
Design and implement a Least Frequently Used (LFU) Cache with the following functionalities:
1. put(U__ID, value): Insert the value in the cache if the key ('U__ID') is not alrea...read more
Ans. 
I used min-heap to implement LFU , as it handles insertion, deletion, and update in logarithmic time complexity. A tie can be resolved by removing the least recently used cache block. I also used an hashmap to store the indices of the cache blocks which allows searching in constant time.

The interviewer was happy with my solution
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Q4. Write a SQL query to find the X percentile of students.
Ans. 
Tip 1 : Practice SQL queries from different websites.
Tip 2 : Use different websites for quick revision of common SQL commands.
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Q5. Can you explain polymorphism and provide examples of real-time and run-time polymorphism?
Ans. 
Tip 1 : Read OOPs concepts thoroughly.
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Round duration - 60 Minutes
Round difficulty - Easy

The overall interview experience was quite smooth and the interviewers were very kind.
I was asked 2 coding questions.

Q1. 
Reverse Doubly Linked List in Groups Problem
You are provided with a Doubly Linked List consisting of integers and a positive integer 'K', which represents the size of the group. Your task is to modify th...read more
Ans. Recursion
The idea is very simple. We will process ‘K’ nodes at a time. Firstly, we will reverse the first ‘K’ nodes of the doubly linked list and then we will do this recursively for the remaining linked list.
Algorithm:
• If the node does not exist, simply return ‘NULL’.
• ‘HEAD’ is pointing to the first node of the linked list.
• If there are less than ‘K’ nodes, just reverse them and return the reversed linked list. Else reve...read more
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Q2. 
Largest Rectangle in Histogram Problem Statement
You are given an array/list HEIGHTS of length N, where each element represents the height of a histogram bar. The width of each bar is considered to be 1.
...read more
Ans. Brute Force
Our intuition is to consider each and every rectangle once so that we can calculate which rectangle has the maximum area.
 
A simple solution to this problem is to one by one consider all bars as starting points and calculate the area of all rectangles starting with every bar and iterating towards the end of the array/list. Finally, return the maximum of all possible areas.
Space Complexity: O(1)Explanatio...read more
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Round duration - 50 Minutes
Round difficulty - Medium

3 coding questions were asked and 1 on system design.

Q1. 
Maximize the Sum Through Two Arrays
You are given two sorted arrays of distinct integers, ARR1 and ARR2. If there is a common element in both arrays, you can switch from one array to the other.
Your task...read more
Ans. Recursive
In this problem, our primary focus is on the common elements i.e. an element that is present in both the arrays. Then, we have to decide whether we have to make a switch. So for that, first we store all the elements of ‘ARR1’ and ‘ARR2’ into ‘MAP1’ and ‘MAP2’ respectively. 
 
Now we call our ‘maximiseSumHelper’ function. We call this function for both cases i.e starting with ‘ARR1’ and starting with ‘A...read more
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Q2. 
Number of Islands Problem Statement
You are provided with a 2-dimensional matrix having N rows and M columns, containing only 1s (land) and 0s (water). Your goal is to determine the number of islands in t...read more
Ans. Flood Fill Algorithm
We can use the flood fill algorithm to check for all connected 1s.
 
• We create two arrays, dx, and dy, in which we store the unit vectors for all eight directions. Thus, when we are at a given cell, we can easily check for all its adjacent cells by simply looping over the two arrays, adding their values to the current position, and checking for this new position recursively.
• We will also create a ...read more
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Q3. How would you design Instagram?
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Round duration - 15 Minutes
Round difficulty - Medium