Dunzo Software Development Engineer Interview Questions and Answers

Q1. Push notifications
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Q2. DATA STRUCTURE with js
Ans. 
Data structures are used to store and organize data in a computer so that it can be accessed and manipulated efficiently.
• Data structures in JavaScript include arrays, objects, sets, and maps.

• Arrays are used to store a collection of elements, accessed by index.

• Objects are used to store key-value pairs.

• Sets are used to store unique values.

• Maps are used to store key-value pairs with keys of any type.
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Q1. Timer in react native
Ans. 
In React Native, timers can be implemented using the setTimeout and setInterval functions.
• Use setTimeout for a one-time delay before executing a function.

• Use setInterval for executing a function repeatedly at a specified interval.

• Remember to clear the timer using clearTimeout or clearInterval when no longer needed.
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Q2. Find occurance of elements in array
Ans. 
Count occurrences of elements in an array of strings
• Iterate through the array and use a hashmap to store the count of each element

• Use a for loop to go through each element and increment the count in the hashmap

• Return the hashmap with element counts
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Q1. Explain Deadlock?
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Deadlock is a situation in computing where two or more processes cannot proceed because each is waiting for the other to release resources.
• Occurs in multi-threaded environments when processes hold resources and wait for others.

• Example: Process A holds Resource 1 and waits for Resource 2, while Process B holds Resource 2 and waits for Resource 1.

• Can lead to system inefficiency and unresponsiveness.

• Deadlock detection and...read more
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Q2. Explain Red Black Tree?
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A Red-Black Tree is a balanced binary search tree with specific properties to ensure efficient operations.
• Each node is colored either red or black.

• The root node is always black.

• Red nodes cannot have red children (no two reds in a row).

• Every path from a node to its descendant leaves must have the same number of black nodes.

• This structure ensures O(log n) time complexity for insertion, deletion, and search operations.

• Exa...read more
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Q3. Find local minima in a 1-D array?
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Q4. Find local minima in 2-D array?
Ans. 
Local minima in a 2-D array are elements smaller than their neighbors. We can find them using various algorithms.
• A local minimum is defined as an element that is less than its adjacent elements.

• For example, in the array [[9, 8, 7], [6, 5, 4], [3, 2, 1]], the element 1 is a local minimum.

• To find local minima, iterate through each element and compare it with its neighbors (up, down, left, right).

• Consider edge cases where...read more
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Round duration - 60 minutes
Round difficulty - Easy

The round consisted of 2 coding Problems and it lasted for 60 minutes from 12:00 PM to 1:00 PM on Hackerearth.
Use of other IDEs was prohibited and video was on.

Q1. 
Implement indexOf Function
You are provided with two strings A and B. Your task is to find the index of the first occurrence of A within B. If A is not found in B, return -1.
Example:
Input:
A = "bc", ...read more
Ans. 
Implement a function to find the index of the first occurrence of one string within another string.
• Iterate through the second string and check if a substring of the same length as the first string matches the first string.

• Return the index of the first occurrence of the first string within the second string, or -1 if not found.

• Handle edge cases like empty strings or when the first string is longer than the second string...read more
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Q2. 
Problem: Search In Rotated Sorted Array
Given a sorted array that has been rotated clockwise by an unknown amount, you need to answer Q queries. Each query is represented by an integer Q[i], and you must ...read more
Ans. 
Search for integers in a rotated sorted array efficiently.
• Implement binary search to find the target integer in the rotated array.

• Handle the rotation by checking which side of the array is sorted before performing binary search.

• Return the index of the target integer if found, else return -1.

• Time complexity of O(logN) is required for each query.
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Round duration - 60 minutes
Round difficulty - Medium

The round was conducted on Google Meet with 2 interviewers . They were friendly and helpful.
The timing was 12:00 to 1:00 PM.
Our Video was on .

Q1. 
Distinct Subsequences Problem Statement
You are given a string 'S' of length 'N' which may include duplicate alphabets. Your goal is to calculate the number of distinct subsequences in the string.
Exampl...read more
Ans. 
Calculate the number of distinct subsequences in a string with possible duplicates.
• Use dynamic programming to keep track of the count of distinct subsequences for each character in the string.

• Consider the cases where the current character is included or excluded in the subsequence.

• Handle duplicates by considering the previous occurrence of the character.

• Return the count of distinct subsequences modulo 10^9 + 7.
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Round duration - 60 minutes
Round difficulty - Easy

This was a Behavioral Round. It lasted for 45-50 minutes. It consisted of a discussion on my projects. The interviewer was very impressed by the way I explained my projects. She even appreciated me for that. This was followed by normal HR questions .Timing of This round was 4:00 PM to 5:00 PM

Sorting of an array and aptitude

Q1. BFS graph traversal
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Q1. Binary tree question
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Basic maths, logical resoning, puzzles

Competitive Programming on Dynamic Programming, Java code debug, SQL qurries

Q1. Hard Stock sell problem
Ans. 
The hard stock sell problem involves determining the best time to sell stocks to maximize profit.
• Consider using dynamic programming to solve this problem efficiently.

• Keep track of the minimum stock price seen so far and calculate the maximum profit that can be made by selling at each day.

• The final answer will be the maximum profit that can be made by selling at the last day.
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Q2. Create a server without express
Ans. 
Creating a server without using Express framework
• Use Node.js built-in 'http' module to create a server

• Listen for incoming requests on a specific port

• Handle different routes and methods using 'http' module
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Q3. What is singleton class, write a usecase through code
Ans. 
Singleton class is a class that can only have one instance created throughout the application.
• Singleton class restricts the instantiation of a class to one object.

• It is often used for logging, caching, thread pools, database connections, etc.

• Example: Java implementation of Singleton class -

• public class Singleton { private static Singleton instance; private Singleton() {} public static Singleton getInstance() { if(insta...read more
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Q1. What is event loop, how it works.
Ans. 
Event loop is a mechanism in programming that allows for asynchronous execution of code by continuously checking for and handling events.
• Event loop is commonly used in JavaScript to handle asynchronous operations like setTimeout, setInterval, and AJAX requests.

• It works by continuously checking the event queue for any pending events, executing them one by one, and then moving on to the next event.

• Event loop helps in pre...read more
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Q2. Micro task queue and macro task queue.
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Q3. Is node.js single threaded or multi-threaded, also discuss threadpool and it's usages.
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Q4. Tell the order of output, among process, promise, setTimeout, fs, setInterval.
Ans. 
The order of output is fs, process, setTimeout, setInterval, promise.
• fs module is synchronous and will output first

• process is next in line

• setTimeout will be executed after process

• setInterval will be executed after setTimeout

• promise will be executed last
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Q1. JavaScript usages compiler or interpreter.
Ans. 
JavaScript is an interpreted language.
• JavaScript is an interpreted language, meaning it is executed line by line at runtime.

• There is no separate compilation step in JavaScript like in languages that use compilers.

• Examples of interpreted languages include Python, Ruby, and PHP.
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Q2. Tell the output among various for loops using var, let and bind.
Ans. 
Output comparison of for loops using var, let, and bind in JavaScript.
• Using var: variable is function-scoped, may lead to unexpected behavior in loops.

• Using let: variable is block-scoped, recommended for loop iterations.

• Using bind: creates a new function with a specified 'this' value and initial arguments.
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Q3. A medium level dsa question on array, solved it using pre-sum.
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Q4. Situation based question, on how to pick a suitable database.
Ans. 
Choosing a database involves evaluating data structure, scalability, consistency, and specific use cases.
• Understand data structure: Use SQL for structured data (e.g., PostgreSQL) and NoSQL for unstructured data (e.g., MongoDB).

• Consider scalability: Choose databases like Cassandra for horizontal scaling in large applications.

• Evaluate consistency needs: Use strong consistency databases like MySQL for critical transaction...read more
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Q1. What do you do on daily basis, and how to decide a tech-stack on high level.
Ans. 
I work on coding, debugging, testing, and collaborating with team members. Tech stack decisions are based on project requirements, scalability, performance, and team expertise.
• Daily tasks include coding, debugging, testing, and collaborating with team members

• Tech stack decisions are based on project requirements, scalability, performance, and team expertise

• Consider factors like language compatibility, libraries/framewo...read more
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Q2. Design an online scalable, real-time document sharing application like google docs.
Ans. 
Design a scalable, real-time document sharing app like Google Docs.
• Use websockets for real-time collaboration

• Implement version control to track changes

• Utilize a distributed database for scalability

• Include user authentication and access control

• Support offline editing with automatic sync
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Q3. How to handle images also in the future.
Ans. 
Utilize cloud storage for scalability, implement image compression techniques, and regularly update image processing libraries.
• Utilize cloud storage for scalability

• Implement image compression techniques

• Regularly update image processing libraries
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Q4. Any other way to solve the problem, of high I/O on same document to overcome throughput and conflicts.
Ans. 
Implement strategies like versioning, sharding, and caching to manage high I/O and reduce conflicts on the same document.
• Use versioning to track changes and allow concurrent edits without conflicts. For example, implement optimistic locking.

• Implement sharding to distribute the load across multiple servers, reducing the I/O on a single document.

• Utilize caching mechanisms to store frequently accessed data in memory, mini...read more
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