Given two linked lists, each representing a number with digits stored in non-reverse order (most significant digit first), add the two numbers and return the sum as a linked list. A critical constraint was that the linked lists cannot be reversed before performing the addition.

I was asked to describe or implement an algorithm to detect the presence of a cycle in a given undirected graph.

Given an array of numbers, which may include zeros, negative numbers, and duplicates, the task was to find the smallest positive integer (greater than 0) that is not present in the array. For example, if the input array is [0, -1, 1, 4, 5], the minimum missing positive number is 2.

Given an array of integers heights representing the histogram's bar height where the width of each bar is 1, find the area of the largest rectangle in the histogram.

Given two sorted integer arrays nums1 and nums2, merge nums2 into nums1 as one sorted array. The number of elements initialized in nums1 and nums2 are m and n respectively. You may assume that nums1 has a size equal to m + n such that it has enough space to hold additional elements from nums2.

You are given an array of k linked-lists, each sorted in ascending order. Merge all the linked-lists into one sorted linked-list and return it.

Explain the fundamental differences between stack memory and heap memory, including how memory is allocated and deallocated in each, their typical use cases, and their performance characteristics.

Discuss the advantages of using std::vector in C++ compared to raw arrays or other dynamic data structures like std::list. Consider aspects such as memory management, performance, and ease of use.

Compare the traversal efficiency of linked lists versus arrays. Explain the underlying memory access patterns and how they affect performance for sequential and random access. Discuss scenarios where one data structure would be preferred over the other for traversal.

Given a string s and an integer k, return the length of the longest substring of s that contains at most k distinct characters.

Design and implement a Least Recently Used (LRU) cache. It should support the following operations: get and put. get(key) will retrieve the value of the key if it exists in the cache, otherwise return -1. put(key, value) will insert the key-value pair or update the value if the key already exists. When the cache reaches its capacity, it should invalidate the least recently used item before inserting a new item.

Explain the concepts of vertical scaling (scaling up) and horizontal scaling (scaling out) in system design. Discuss their advantages, disadvantages, appropriate use cases, and limitations.

Describe how you would architect or implement measures to prevent or mitigate a Distributed Denial of Service (DDoS) attack from significantly impacting your software or system. Discuss various layers of defense.

Discuss key concepts in system design including Microservices architecture, Load Balancing techniques, and Master-Slave architecture for databases. Explain their purposes, benefits, drawbacks, and how they contribute to a robust and scalable system.

Tell me about yourself, highlighting your background, experience, and what brings you to this interview.

What all projects have you worked on? Be prepared to discuss your contributions, the technologies used, challenges faced, and outcomes achieved for relevant projects.

Describe a situation where you had a conflict with a team member. How did you handle it, and what was the outcome? What did you learn from the experience?

How do you typically receive and respond to feedback from your manager, both positive and constructive? Can you share an example of how you used feedback to improve?

How do you rate yourself in Java on a scale from 1 to 10? Based on your self-assessment, what specific steps would you take to further improve your Java skills?

Describe your proudest moment or accomplishment in your career. What made it significant, and what was your role in achieving it?

What is the most recent skill or technology you have learned? Why did you decide to learn it, and how have you applied it?

What challenges did you face at the beginning of your career, and how did you overcome them? What lessons did you learn from those experiences?

Describe how you handle pressure and manage a high workload effectively. Can you provide an example of a time you successfully navigated a demanding period?

How do you define success in a professional context, both for yourself and for a team or project?

Explain how your past projects or contributions have directly benefited or positively impacted users or stakeholders.

This is your opportunity to ask questions to the interviewer about the role, team, company culture, or next steps.

Given a binary tree, find the lowest common ancestor (LCA) of two given nodes p and q. This initial understanding of the problem assumed both nodes are guaranteed to be present in the tree. (Referenced as LeetCode #236)

A clarification to the initial LCA problem: the given nodes p and q may or may not be present in the tree. If only one node is present, that node is considered the LCA. If neither is present, the function should return null. (This problem variation was referenced as LeetCode #1644, which typically deals with scenarios like parent pointers or BSTs where nodes might not exist, but the core requirement here was handling optional node presence).

Given an array of characters, compress it in-place. The length after compression must always be less than or equal to the original array. Every element of the array should be a character (not int) of length 1. After you are done modifying the input array in-place, return the new length of the array.

Given two strings representing numbers, for example, a = "120" and b = "45", write a function to add them as if they were actual numbers and return their sum as a string. You are not allowed to convert the strings to integers directly.

Discuss the key features and characteristics of the Java programming language.

Provide a detailed discussion on the Java Collections Framework, including its interfaces, core classes, and common use cases.

Explain the fundamental differences between Java's ArrayList and a primitive array, covering aspects such as type safety, resizing, and performance.

Describe the internal working mechanisms of Java's HashMap, including concepts like hashing, collision resolution (e.g., chaining/open addressing), and resizing.

Discuss fundamental concepts related to Multithreading in Java, such as threads, processes, synchronization mechanisms (locks, semaphores, monitors), and potential concurrency issues.

Explain the concepts of Virtual Memory, Thrashing, and Semaphores within the context of Operating Systems.

Discuss the ACID properties in database transactions and explain different approaches to find the Nth highest salary in a database.

Design a method that inherently has failure points and discuss strategies to make it more robust and resilient in a production environment.

Given a string of parentheses, return the number of braces required to be inserted to make the parentheses valid. Example: ()))(( -> 4 (because ()()()()()), ((())) -> 0. Note: () is valid but )( is invalid. Similar to LeetCode's Score of Parentheses.

Given an array of integers and a target sum k, find a pair of elements in the array that sum up to k. If using a map approach, handle duplicate elements. Example: I/p: 1, 2,5, 4, 3 K=7 -> O/p: 2,5. I/p 2 : 3, 4, 1 k=6 -> Output: empty. I/p 3: 3, 2, 4, 3, 1, 3 k=6 -> O/p: 3,3. Similar to LeetCode's Two Sum.

Given a binary tree, print all peripheral nodes (boundary nodes) of the tree in clockwise order.

			4
         /   \
        6     9
      /  \     \
     3    1     0
    / \    \   /  \
   4   2    4 8   3
       /         /
      5         7
                 \
                  1
                   \
                    2

Expected Output: 4,3,6,4,9,0,3,7,8,4,5. Similar to LeetCode's Boundary of Binary Tree.

Given a default index array (0,1,2,3,4,5,6,7,...) and an int[] array where int[i] gives the next index. Find a cycle and print the node count within that cycle. Examples: int[]-> 2,4,4,5,0,8,9,6 -> 3, int[]-> 2,4,4,5,5,6,2,6 -> 4.

Explain what lambda expressions are and how to write them in Java.

Discuss Java Streaming API, including what streaming is and its different types.

Given an integer array, write a method to return the count of even and odd integers using Java Lambda expressions or the Streaming API.

Explain the difference between float and double data types in Java.

Discuss the backend logic for implementing a fund switch system. Specifically, would you handle it in one transaction or two?

For handling multiple transactions, would you process them in parallel or one by one?

Design a Vending Machine with the following user roles:

• Operator: Refill Vending Machine, Take Money
• Administrator: Control Vending Machine Administrative Tasks (e.g., Product Management, Machine Configuration like Products Supported, Money), User Roles/Password
• End User (Customer): View Product, Select Product, Buy. Methods to Accept Money From End User, Perform Validation and Return Back Amount (if applicable).

Primary Requirements:

• Should support RBAC Validation.
• Support Administrator Functions like Product Management, Money Control, RBAC.
• Support End User functions (Allow User to View Product, Select Product and Buy - Method To Accept Money From End User, Perform Validation and Return Back Amount if applicable).

Secondary Requirements:

• How to extend this to support Multiple User Roles, Product, and Currency.
• NFRs like Scale.
• How to Manage Vending Machine Configuration from a Central Location (Configuration Like - Products Supported, Current Availability, State).

Discuss the Usage of SOLID Principles and Design Patterns.

How to write Many-to-Many annotations in JPA. Provide end-to-end code for JPA with a Many-to-Many relation, specifically for multiple students selecting multiple subjects. The candidate mentions keeping it simple with a relation table rather than using Many-to-Many relation annotation usage directly.

Discussion on authentication and authorization. What do you pass to validate a request (e.g., username/password/token)? How do you assure that an incoming request is a valid request?

Given a Spring Boot code snippet:

@Component
Interface I1
class A implements I1
Class B implements I2
main() {
@Autowired
I1 i;
//Will this compile, if not then what can make this work
//Requirement is to inject only class A

The expected solution is to achieve this through @Inject on the class level.

Given two sorted arrays, a and b.

a = 10, 11, 22
b = 6, 8, 12, 24

The task is to form combinations adhering to these rules:

• Both arrays are sorted.
• First element should be from A.
• Last element should be from B.
• Combination should be in ascending order.
• Elements have to be subsequent from each array.

Expected Output:

10, 12
10, 12, 22, 24
10, 24

11, 12
11, 12, 22, 24
11, 24
22, 24