The interview process for Walmart Labs consisted of 3 technical rounds and 1 managerial round. The overall process was very smooth.

1st Round: Data Structures

The interviewer was good and covered topics such as linked lists, arrays, and strings. The session began with introductions and a discussion about my projects and previous organization. Following this, I was asked to write a program to add two linked lists. Next, the interviewer moved to string-related questions, asking for a program to find the first element with a frequency of three.

2nd Round: Java

This round focused heavily on multi-threading. The interviewer seemed primarily interested in a specific, predefined approach rather than exploring all possible solutions. The questions included:

• Writing a custom Blocking Queue (Producer-Consumer problem)
• Internals of ConcurrentHashMap
• Questions on future, callable, and ThreadExecutor
• Writing code to make a class immutable
• Several questions related to Java collections

3rd Round: Java and Problem Solving

The interviewer was quite serious and offered minimal assistance when I encountered difficulties. The round started with a program to balance brackets, which I had to write and execute. Afterward, we moved to Java questions:

• What is special about Strings in Java? How does the String pool work?
• Writing a thread-safe singleton class
• Comparable vs. Comparator
• wait vs. sleep in threads
• How Blocking Queues work
• A SQL query (the exact question was not recalled due to a background in NoSQL)
• Indexing in databases
• Writing a program to reverse a linked list

4th Round: Managerial

The interviewer was approachable and began with a greeting. He asked me to draw the architecture diagram for a project from my previous organization and posed a few questions about it. The discussion then shifted to design questions, including designing an HTML file parser and other design patterns. Finally, the interviewer provided information about the team I would be joining.

Add two linked lists.

Character frequency in a string.