Zolo Software Engineer Interview Questions and Answers

Q1. Build an sample app server with express.js
Ans. 
Build a sample app server using express.js
• Install express.js using npm

• Create a new express app

• Set up routes and middleware

• Start the server to listen on a specific port
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Q2. How do you make connection with database in your project
Ans. 
I use JDBC (Java Database Connectivity) to establish connection with the database in my project.
• Use JDBC API to connect to the database

• Load the JDBC driver

• Create a connection object

• Create a statement object

• Execute SQL queries
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Q3. Write multer middleware code.
Ans. 
Multer is a middleware for handling multipart/form-data, used for file uploads in Node.js.
• Install multer package using npm: npm install multer

• Require multer in your Node.js file: const multer = require('multer')

• Set up multer middleware with desired options: const upload = multer({ dest: 'uploads/' })

• Use the upload middleware in your route handler to process file uploads
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2 Graph question of leetcode

Q1. DSA Questions of leetcode
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Q2. DSA Questions
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Sorting of an array and aptitude

Q1. BFS graph traversal
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Q1. Binary tree question
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Round duration - 60 Minutes
Round difficulty - Medium

It has 3 Coding Questions of medium-hard level and the time limit was 1 hour only. I don’t exactly remember the questions but I was able to do only two of them completely.

Q1. 
Biggest Number Formation Problem
Your task is to construct the largest number possible by concatenating each of the provided positive integers in the array exactly once.
Input:
Integer T denoting the nu...read more
Ans. 
Construct the largest number by concatenating positive integers in the array exactly once.
• Sort the array of integers in a way that the concatenation of the numbers forms the largest possible number.

• Use a custom comparator function to sort the numbers based on their concatenated values.

• Join the sorted array elements to form the final largest number.
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Q2. 
Number of Longest Increasing Subsequence Problem Statement
Given an integer array ARR of length N, determine the count of longest increasing subsequences present in the array.
Explanation:
The Longest I...read more
Ans. 
Count the number of longest increasing subsequences in an integer array.
• Identify the longest increasing subsequences in the array

• Count the number of such subsequences

• Consider the constraints while implementing the solution

• Examples: For input [50, 3, 90, 60, 80], the output is 2
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Round duration - 60 Minutes
Round difficulty - Medium

First, the interviewer introduced himself and then asked to introduce myself. Then he asked about the projects I did. After an introductory discussion on projects, he gave me 3 coding questions on their personal live code environment.

He asked me to explain the approach first and then code it down. I had to explain the time complexity of each solution and optimal code if possible with lesser time complexity.

Q1. 
Cache Operations Problem
You are provided with a cache that can hold a maximum of 'N' elements. Initially, this cache is empty. There are two main operations you can perform on this cache:
Explanation:
...read more
Ans. 
Implement a cache with insert, update, and retrieve operations, returning results of retrieve operations in order.
• Create a cache data structure with specified size 'N'.

• Implement insert and update operations based on the given criteria.

• For retrieve operation, return the value associated with the 'U_ID' if present, else return -1.

• Handle cases where the cache is full and least frequently used items need to be removed.

• Retu...read more
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Q2. 
Possible Words from a Phone Number: Problem Statement
Given a string S composed of digits ranging from 2 to 9, determine all possible strings that can be created by mapping these digits to their correspon...read more
Ans. 
Given a phone number, generate all possible words by mapping digits to letters on a T9 keypad.
• Create a mapping of digits to letters on a T9 keypad

• Use recursion to generate all possible combinations of letters for the given phone number

• Sort the resulting strings in lexicographical order
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Q3. 
Shortest Unique Prefix Problem
You are given an array containing N words. Your task is to derive the shortest prefix for each word that uniquely identifies it amongst the other words. For instance, given t...read more
Ans. 
Given an array of words, find the shortest unique prefix for each word.
• Create a Trie data structure to efficiently store and search for prefixes.

• Traverse the Trie to find the shortest unique prefix for each word.

• Return the list of shortest unique prefixes for all words.
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Round duration - 60 Minutes
Round difficulty - Hard

In this round interviewer gave me 2 coding questions and asked me to code on any editor of my choice. I opened VS code to code those problems.

Q1. 
Maximum Subarray Sum Problem Statement
Given an array arr of length N consisting of integers, find the sum of the subarray (including empty subarray) with the maximum sum among all subarrays.
Explanation...read more
Ans. 
Find the sum of the subarray with the maximum sum among all subarrays in a given array.
• Iterate through the array and keep track of the maximum sum subarray seen so far.

• Use Kadane's algorithm to efficiently find the maximum subarray sum.

• Handle cases where all elements are negative by returning the maximum element in the array.

• Consider the sum of an empty subarray as 0.
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Q2. 
LRU Cache Implementation
Design and implement a data structure for the Least Recently Used (LRU) cache, which supports the following operations:
1. get(key) - Return the value associated with the key if ...read more
Ans. 
Implement a Least Recently Used (LRU) cache data structure with get and put operations.
• Use a combination of a hashmap and a doubly linked list to efficiently implement the LRU cache.

• Keep track of the least recently used item and remove it when the cache reaches its capacity.

• Update the position of an item in the cache whenever it is accessed or updated.

• Ensure constant time complexity for both get and put operations by u...read more
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Round duration - 40 Minutes
Round difficulty - Easy

The interviewer was very friendly. He asked me about myself and previous interviews.

Round duration - 90 minutes
Round difficulty - Medium

There were a total of 3 coding questions to be solved, and the time limit was 90 minutes. The candidate was free to use language of their choice.

Q1. 
Longest Palindromic Subsequence Problem Statement
Given a string A consisting of lowercase English letters, determine the length of the longest palindromic subsequence within A.
Explanation:
• A subsequ...read more
Ans. 
The task is to find the length of the longest palindromic subsequence in a given string.
• A subsequence is a sequence generated from a string after deleting some or no characters of the string without changing the order of the remaining string characters.

• A string is said to be palindrome if the reverse of the string is the same as the actual string.

• Find the longest palindromic subsequence by considering all possible subs...read more
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Round duration - 45 minutes
Round difficulty - Easy

The first round of interview lasted for around 45 minutes. I was asked two DSA questions, and was supposed to code them while my screen was shared. I wrote code for both the questions with little help from the interviewer. Finally, I was asked couple of questions based on my resume.

Q1. 
Merge Two Sorted Linked Lists Problem Statement
You are provided with two sorted linked lists. Your task is to merge them into a single sorted linked list and return the head of the combined linked list.
...read more
Ans. 
The task is to merge two sorted linked lists into a single sorted linked list.
• Create a new linked list to store the merged list

• Compare the values of the nodes from both lists and add the smaller value to the new list

• Move the pointer of the list with the smaller value to the next node

• Repeat the comparison and addition until one of the lists is empty

• Add the remaining nodes from the non-empty list to the new list

• Return th...read more
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Q2. 
Rotational Equivalence of Strings Problem Statement
Given two strings 'P' and 'Q' of equal length, determine if string 'P' can be transformed into string 'Q' by cyclically rotating it to the right any num...read more
Ans. 
The task is to check if one string can be converted into another string by cyclically rotating it to the right any number of times.
• Iterate through each character of the first string and check if it matches the corresponding character in the second string after a certain number of cyclic rotations.

• If all characters match for any number of cyclic rotations, then the first string can be converted into the second string.

• Us...read more
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Round duration - 30 minutes
Round difficulty - Medium

I was given one data structure question and was then asked about recursion.

Q1. 
Next Greater Element Problem Statement
You are provided with an array or list ARR containing N positive integers. Your task is to determine the Next Greater Element (NGE) for each element in the array.
T...read more
Ans. 
The task is to find the next greater element for each element in an array.
• Iterate through the array from right to left

• Use a stack to keep track of the elements

• For each element, pop elements from the stack until a greater element is found or the stack is empty

• If a greater element is found, it is the next greater element for the current element

• If the stack becomes empty, there is no greater element to the right

• Store the ...read more
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Round duration - 40 minutes
Round difficulty - Easy

This was the hiring manager round. No data structures question were asked in this round. There was discussion around the projects that I had done and my resume. As I am from EEE branch, I was asked why I want to get into software. The interview happened around 8 PM. I was asked to create a schema for one of my projects.

Q1. Why do you want to pursue a career in software?
Ans. 
I want to get into software because of my passion for problem-solving and the opportunity to create innovative solutions.
• Passion for problem-solving

• Opportunity to create innovative solutions

• Interest in technology and its impact on society

• Career growth and job stability

• Flexibility and remote work options
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Q1. The question was about Nodejs
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Q2. The question was to build a linked list in Nodejs
Ans. 
A linked list in Node.js is a data structure consisting of nodes that hold data and a reference to the next node.
• A linked list consists of nodes, each containing data and a pointer to the next node.

• To create a linked list, define a Node class with properties for data and next.

• Implement methods to add, remove, and traverse nodes in the linked list.

• Example of adding a node: function add(value) { const newNode = new Node(...read more
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Q1. The first question was related to DSA
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Q2. The question was related to SQL
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Basic coding only not to worry much

Q1. Tell me about ur self
Ans. 
I am a passionate software developer with experience in Java, Python, and web development.
• Experienced in Java, Python, and web development technologies

• Strong problem-solving skills

• Excellent team player with good communication skills
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Q2. What is ur projects
Ans. 
I have worked on various projects including a web-based inventory management system and a mobile app for tracking fitness goals.
• Developed a web-based inventory management system using React and Node.js

• Created a mobile app for tracking fitness goals using Flutter

• Implemented RESTful APIs for communication between frontend and backend systems
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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