Perfios Software Solutions Interview Questions and Answers

4 DSA questions and aptitude questions. It was a pen and paper test for nearly 75 to 90 min

Q1. DBMS fundamental questions
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Q2. Variation of repeating DNA sequences LC question.
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Q3. DB Schema and API design of my internship work.
Ans. 
Designed DB schema and API for internship project
• Created normalized database schema to store user information, orders, and products

• Implemented RESTful API endpoints for CRUD operations on user data

• Used authentication and authorization mechanisms to secure API endpoints

• Optimized queries for efficient data retrieval and processing
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Q1. Fundamental OS questions
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Q2. Basic stack questions
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Q1. Strings question. Had to do this in O(1) TC and O(1) SC
Ans. 
Determine if a string has all unique characters in O(1) time and space.
• Use a fixed-size array of 256 (for ASCII) to track character occurrences.

• Iterate through the string, marking characters in the array.

• If a character is found twice, return false; otherwise, return true.

• Example: 'abc' -> true, 'aabc' -> false.
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Q2. Extensive discussion on internship experiences
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Q1. How do alarm clock work in phones
Ans. 
Alarm clocks in phones work by triggering a pre-set notification at a specific time to alert the user.
• Alarm clock app is programmed to trigger a notification at a specific time set by the user

• The phone's system clock is used to track the current time and compare it to the set alarm time

• When the alarm time matches the current time, the phone plays the selected alarm sound or vibration

• Users can customize alarm settings s...read more
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Q2. Real life application of DSA
Ans. 
Data Structures and Algorithms are used in real life applications such as social media algorithms, GPS navigation, and search engines.
• Social media algorithms use DSA to personalize user feeds based on their interests and interactions.

• GPS navigation systems use Dijkstra's algorithm to find the shortest route between two locations.

• Search engines like Google use algorithms like PageRank to rank web pages based on relevanc...read more
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Q1. Given an array, how can you rotate it by n positions?
Ans. 
Rotate an array of strings by n positions
• Create a new array and copy elements from original array starting from index n to the end, then copy elements from index 0 to n-1

• Alternatively, you can use array slicing to achieve the rotation

• Example: Original array ['a', 'b', 'c', 'd', 'e'], rotate by 2 positions would result in ['c', 'd', 'e', 'a', 'b']
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Q2. Prepare basic OOPS concepts
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Q3. Last entry of a table in sql query
Ans. 
Use ORDER BY and LIMIT to get last entry in SQL query
• Use ORDER BY column_name DESC to sort in descending order

• Use LIMIT 1 to get only the last entry
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Q1. Internal functioning of hash map
Ans. 
Hash map is a data structure that stores key-value pairs and uses a hash function to map keys to their corresponding values.
• Hash map uses a hash function to determine the index of the key-value pair in the underlying array.

• Collisions can occur when two keys hash to the same index, which can be resolved using techniques like chaining or open addressing.

• Hash maps offer constant time complexity O(1) for insertion, deletio...read more
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Q2. What is the implementation of a palindrome check in Java without using the reverse() function?
Ans. 
Implementing a palindrome check in Java without using the reverse() function.
• Create a function that takes a string as input.

• Use two pointers, one starting from the beginning of the string and the other from the end.

• Compare characters at the two pointers and move them towards each other until they meet or cross.

• If all characters match, the string is a palindrome.

• Example: 'racecar' is a palindrome.

• Example: 'hello' is not...read more
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Q1. Sorting arrays from 0's,1 in java , No sorting algorithm to be used Difficulty: Easy
Ans. 
Use counting method to sort array of strings with 0's and 1's.
• Create a count array to store the frequency of 0's and 1's.

• Update the original array based on the count array.

• Example: Input array - ['0', '1', '0', '1', '1'], Output array - ['0', '0', '1', '1', '1']
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Q2. Difference between HTTP vs HTTPS indication
Ans. 
HTTPS provides secure communication over the internet using encryption, while HTTP does not.
• HTTPS uses SSL/TLS encryption to secure data transmission, while HTTP does not.

• HTTPS URLs begin with 'https://' and use port 443, while HTTP URLs begin with 'http://' and use port 80.

• HTTPS ensures data integrity and authentication, while HTTP does not provide these security measures.
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Q3. What is the algorithm to reverse a singly linked list?
Ans. 
The algorithm to reverse a singly linked list involves iterating through the list and changing the pointers to reverse the direction of the links.
• Start with three pointers: current, previous, and next.

• Iterate through the list, updating the next pointer to point to the previous node.

• Move the previous pointer to the current node and the current pointer to the next node.

• Continue until the end of the list is reached, then ...read more
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Q4. Write a SQL query for employee table having
Ans. 
SQL query to retrieve data from employee table
• Use SELECT statement to retrieve data

• Specify the columns you want to retrieve

• Use FROM clause to specify the table name

• Add any conditions using WHERE clause if needed
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Q1. WHat are reacthooks?
Ans. 
React Hooks are functions that let you use state and other React features without writing a class.
• React Hooks were introduced in React 16.8.

• They allow you to use state and other React features in functional components.

• Some commonly used React Hooks are useState, useEffect, useContext, etc.
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Q2. How react is better that JS?
Ans. 
React is better than plain JavaScript for building complex user interfaces due to its component-based architecture and virtual DOM.
• React allows for easier management of state and props through its component-based architecture.

• Virtual DOM in React helps improve performance by only updating the necessary parts of the actual DOM.

• React's declarative approach simplifies the process of building and maintaining complex UIs.

• Re...read more
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DSA : LL, Stack , Trees, BST based questions

5 MySQL queries