400+ Backend Developer Interview Questions and Answers

Vertical order traversal of a binary tree is required to be implemented for given input format and constraints.

• Implement a function to perform vertical order traversal of a binary tree

• Maintain the order of nodes based on their positions (X, Y)

• Handle cases where two nodes have the same position by considering the left node first

• Follow the input and output format as specified in the question

Calculate the sum of all elements in an array of length N.

• Read the size of the array N and then read N integers as elements of the array.

• Iterate through the array and add each element to a running sum.

• Return the final sum as the output.

The minimum number of weighings necessary is 2.

• Divide the 9 balls into 3 groups of 3.

• Weigh any two groups against each other.

• If the two groups weigh the same, the heavier ball is in the third group.

• If one group is heavier, the heavier ball is in that group.

• Take the heavier group and weigh any two balls against each other.

• If they weigh the same, the heavier ball is the remaining one.

• If one ball is heavier, it is the heavier ball.

Remove duplicate occurrences of characters in a given string.

• Use a hash set to keep track of characters seen so far.

• Iterate through the string and add non-duplicate characters to a new string.

• Return the new string without duplicate characters.

Reverse the order of elements in each row of a given matrix.

• Iterate through each row of the matrix

• Reverse the elements in each row

• Return the modified matrix

Reverse a singly linked list of integers and return the head of the reversed linked list.

• Iterate through the linked list and reverse the pointers to point to the previous node instead of the next node.

• Keep track of the previous, current, and next nodes while reversing the linked list.

• Update the head of the reversed linked list as the last node encountered during the reversal process.

Detect if there exists a cycle in an undirected graph.

• Use Depth First Search (DFS) to traverse the graph and detect cycles.

• Maintain a visited set to keep track of visited vertices.

• If a visited vertex is encountered again during DFS, a cycle exists.

• Return 'Yes' if a cycle is found, 'No' otherwise.

Object-oriented programming (OOP) is a programming paradigm based on the concept of objects.

• OOP is based on the four pillars: encapsulation, inheritance, abstraction, and polymorphism.

• Encapsulation is the practice of hiding data and methods within a class.

• Inheritance allows a class to inherit properties and methods from a parent class.

• Abstraction is the process of hiding implementation details while showing only the necessary information to the user.

• Polymorphism allows object...read more

Java is considered an Object Oriented Programming Language because it supports the key principles of OOP such as encapsulation, inheritance, and polymorphism.

• Java allows for the creation of classes and objects, which are the building blocks of OOP.

• It supports encapsulation by allowing data hiding within classes.

• Inheritance is supported in Java, allowing classes to inherit attributes and methods from other classes.

• Polymorphism is achieved through method overloading and overrid...read more

Sort an array of 0's, 1's, and 2's using two pointer approach.

• Initialize two pointers, one at the beginning and one at the end of the array.

• Traverse the array and swap 0's to the beginning and 2's to the end using the pointers.

• Stop when the pointers meet or cross each other.

Search for an element in a rotated sorted array using binary search with pivot.

• Find the pivot element using binary search.

• Compare the target element with the first element of the array to determine which half to search.

• Perform binary search on the selected half of the array.

• Repeat until the target element is found or the array is exhausted.

I will ensure that our code is properly protected by implementing security measures and legal actions if necessary.

• Implement security measures such as encryption and access control to prevent unauthorized access to our code.

• Monitor for any suspicious activity and take immediate action if any unauthorized access is detected.

• If necessary, take legal action against the rival company for intellectual property theft.

• Collaborate with legal and management teams to ensure that our co...read more

Spring Boot offers advantages like rapid development, easy configuration, embedded servers, production-ready features, and more.

• Rapid development: Spring Boot simplifies the setup and configuration of Spring applications, allowing developers to focus on writing business logic.

• Easy configuration: Spring Boot provides auto-configuration, reducing the need for manual setup and boilerplate code.

• Embedded servers: Spring Boot comes with embedded servers like Tomcat, Jetty, and Unde...read more

Backend Developer interview question on Leetcode problems related to arrays and number manipulation.

• Q1: Find number of ways where the square of numbers is equal to the product of 2 numbers

• Q2: Solve a medium-level Leetcode problem based on arrays

• Use appropriate data structures and algorithms to optimize solutions

• Practice problem-solving skills regularly to improve efficiency

package.json lists dependencies and package-lock.json ensures consistent installs.

• package.json lists all the dependencies required for the project

• package-lock.json ensures that the same versions of dependencies are installed across all environments

• package.json is manually edited while package-lock.json is generated automatically

• package-lock.json is used for reproducible builds

Linked list is a linear data structure while tree is a hierarchical data structure.

• Linked list is used when we need to maintain a sequence of elements and perform operations like insertion and deletion at any position.

• Tree is used when we need to represent a hierarchical structure and perform operations like searching, insertion, and deletion efficiently.

• Linked list has a single pointer to the next node while tree has multiple pointers to its child nodes.

• Linked list has a lin...read more

Count distinct ways to climb n steps by climbing 1 or 2 steps at a time, with the ability to skip steps.

• Use dynamic programming to solve this problem efficiently.

• Define a recursive function to calculate the number of ways to climb to the top.

• Consider base cases where n is 0, 1, or 2 for easy calculation.

• Example: For n = 3, there are 3 distinct ways: 1+1+1, 1+2, 2+1.

Find unique combinations of candidate numbers that sum to target, each number can be used only once.

• Use backtracking to explore all possible combinations

• Sort the candidates array to avoid duplicate combinations

• Skip duplicates while exploring combinations to ensure uniqueness

Interview questions for Backend Developer role covering Python and Django

• Python features: dynamic typing, garbage collection, high-level data structures, etc.

• List vs Tuple: List is mutable, Tuple is immutable

• Inheritance: a way to create a new class from an existing one, inheriting its attributes and methods

• Types of inheritance: single, multiple, multilevel, hierarchical

• Self keyword: refers to the instance of the class, used to access its attributes and methods

• Average of numbe...read more

Use two pointers to swap non-zero elements with zero elements in place.

• Use two pointers, one for non-zero elements and one for zero elements.

• Swap non-zero elements with zero elements in place.

• Maintain the order of non-zero elements while moving them to the beginning of the array.

Indexing and partitioning are techniques used in DBMS to improve performance by organizing data efficiently.

• Indexing involves creating an index on a column in a database table to speed up data retrieval. It works like an index in a book, allowing the database to quickly locate the desired data.

• Partitioning involves dividing a large table into smaller, more manageable parts called partitions. This can improve query performance by reducing the amount of data that needs to be sc...read more

Create an Alarm Clock with OOPS, showing current date/time, snooze function, and ability to add/delete alarms.

• Create a class for AlarmClock with properties like currentDateTime, alarmsList

• Implement methods for displaying current date/time, setting alarms, snooze function, adding/deleting alarms

• Use OOPS concepts like encapsulation, inheritance, polymorphism for efficient code structure

Mongo query to increase age by 20% for documents with age field

• Use $exists operator to filter documents with age field

• Use $mul operator to increase age by 20%

• Example: db.users.updateMany({ age: { $exists: true } }, { $mul: { age: 1.2 } })

The design approach of Amazon e-commerce application involves efficient processing of user queries and displaying results. Questions on servlets, Hibernate, and Spring Boot are likely to be asked.

• Amazon e-commerce application likely uses a combination of search algorithms, caching mechanisms, and distributed systems to process user queries efficiently.

• Questions on servlets may involve understanding how they handle HTTP requests and responses in a web application.

• Questions on ...read more

The rules for parcel delivery time estimation should be decoupled from the service for better maintainability and flexibility.

• Decoupling the rules from the service allows for easier maintenance and updates without affecting the service itself.

• Separating the rules also enables reusability across different services or components.

• Using a separate rules engine or configuration file can provide flexibility to adjust the delivery time estimation logic without changing the service c...read more

Search an element in an infinite sorted array using binary search.

• Initialize low as 0 and high as 1.

• Double the high index until arr[high] is greater than the target element.

• Perform binary search between low and high indexes.

Design a stack that supports getMin functionality to return the minimum element in the stack.

• Create two stacks, one for storing the actual elements and another for storing the minimum elements.

• Push elements onto both stacks simultaneously.

• When popping an element, pop from both stacks.

• To get the minimum element, peek at the top of the minimum stack.