thread count coding question leetcode java

I was recently asked a question related to multithreading in java by Morgan Stanley, Q. Imaging you have a List of ids(Integer). Now, a thread is adding new ids in the background and your task is to find if a given id exists or not in the list, taking into account the thread that is regularly adding new values (return true or false).

reddit.com › r/leetcode › need help with a question i came across recently in a test

r/leetcode on Reddit: Need help with a question I came across recently in a test

October 16, 2023 -

I was able to come up with a graph traversal solution but couldn't get all the test cases.

Question:

There are service_nodes of different micro-services in a system with bidirectional connections in the form of a tree (acyclic graph), where the ith edge connects the micro-services service_from[i] and service_to[i]. Each micro-service is configured with a maximum number of live threads that can be present in its lifecycle, where the ith micro-service can have a maximum of threads[i] threads. The micro-services adjacent to each other must have maximum threads differing by exactly 1.

Some configurations were lost, and only k of the micro-services are known. This information is given as a 2D array, currentValues, of size k x 2 denoting [micro-service index, maximum threads], or, [i, threads[i]]

Find the maximum number of live threads that each micro-service can have such that the total number of live threads in the system is the minimum possible. Return an array of length service nodes where the element denotes the maximum number of live threads for the micro-service.

Note: It is guaranteed that the solution always exists.

Constraints 1 <= node_count <= 10⁵ number of given values for nodes <= node_count 1 <= value of a node <= 10⁵

Example

given graph => (1:3)-(2:x)-(3:x)-(4:x)-(5:3) node 1 to 5 (given) for nodes 1 and 5, we have been given the max thread value as 3 and 3, respectively we need to find all x values such that max sum is minimum and adjacent nodes differ by 1 solution for the above graph => (1:3)-(2:2)-(3:1)-(4:2)-(5:3) so we return [3,2,1,2,3]

Videos

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LeetCode Concurrency | Print In Order

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reddit.com › r/leetcode › multi threading questions in interviews

r/leetcode on Reddit: Multi Threading Questions In Interviews

January 22, 2025 -

Why has the concept of multi threading starting to become so ubiquitous and important in interviews? How does one prepare for them ? I have no idea about it being a non CS graduate!

Top answer

1 of 2

If you have enough time and want to do basics for beginners - start reading about POSIX threads and how their language specific implementation works. Read Processes and threads chapter from Modern Operating Systems by Andrew Tanenbaum and pay special attention to Mutex, Semaphore, Condition Variables, Thread Pools, Locks (Spinlocks, Reader-Writer Locks), thread safety, race conditions etc Once you are theoretically familiar with all the core multi-threading patterns (there are 3-4, google them), start doing problems on "multithreading", "concurrency". It is a beautiful concept and widely used in the industry.

2 of 2

I extensively use multithreading in my current job. Large codebases use multithreading/parallel programming a lot. You can checkout software construction course on MIT OCW. It is a very good course that will give you a practical experience in Java.

YouTube

youtube.com › watch

All Leetcode Multithreading questions solved - YouTube

27:36

In this video I have discussed solutions to all multithreading questions present on leetcode.Implemented in C++17https://leetcode.com/problems/print-in-order...

Published June 11, 2023

LeetCode

leetcode.com › discuss › general-discussion › 783299 › problems-on-concurrency-and-multi-threading

Problems on Concurrency and Multi-threading. - Discuss - LeetCode

Problems on Concurrency and Multi-threading.

LeetCode

leetcode.com › problems › print-in-order

Print in Order - LeetCode

Print in Order - Suppose we have a class: public class Foo { public void first() { print("first"); } public void second() { print("second"); } public void third() { print("third"); } } The same instance of Foo will be passed to three different ...

LeetCode

leetcode.com › discuss › interview-question › operating-system › 124639 › how-tobest-practices-to-write-a-thread-safe-code

How to/best practices to write a thread safe code? - Discuss - LeetCode

October 13, 2019 - How to/best practices to write a thread safe code? Also how to identify if a code is thread safe or not?

LeetCode

leetcode.com › problemset › concurrency

LeetCode - The World's Leading Online Programming Learning Platform

Level up your coding skills and quickly land a job. This is the best place to expand your knowledge and get prepared for your next interview.

reddit.com › r/leetcode › resources for must knows of java multithreading/concurrency

r/leetcode on Reddit: Resources for must knows of Java Multithreading/Concurrency

October 24, 2021 -

Okay, I have read/watched jevkov's videos and blogs. But how can i prepare for FAANG interviews? Last time, this interviewer from Goldman had me trippin' answering questions regarding why use singleton pattern, and what occasion I should use multi-threading. But at my job, I did notice there were tests that implements Runnable interface that is multithreaded, and threadcontext on the controller level. So Im not really exposed to multithreading.

Could someone please share some concise resources that gives insights into must know fundamentals of Java Multithreading/concurrency to prepare for FAANG interviews? Thanks

Top answer

1 of 1

Educative.io's multithreading course is a very good resource to prepare for Multi-threading concepts in interviews and even has Multi-threading interview sample problems: https://www.educative.io/courses/java-multithreading-for-senior-engineering-interviews

Find elsewhere

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Medium

medium.com › acing-the-software-engineer-interview › interview-practice-problem-for-multithreading-8f3830cce844

Interview Practice Problems for Multithreading | by LiveRunGrow | Acing the Software Engineer Interview | Medium

June 14, 2023 - When you use the synchronized keyword in Java, it provides built-in locking mechanism to ensure that only one thread at a time can execute the synchronized block or method.

AlgoMonster

algo.monster › liteproblems › 1242

1242. Web Crawler Multithreaded - In-Depth Explanation

In-depth solution and explanation for LeetCode 1242. Web Crawler Multithreaded in Python, Java, C++ and more. Intuitions, example walk through, and complexity analysis. Better than official and forum solutions.

Blogger

javarevisited.blogspot.com › 2014 › 07 › top-50-java-multithreading-interview-questions-answers.html

Top 50 Java Thread and Concurrency Interview Questions Answers for 2 to 5 Years Experienced

See my blog post on the same topic for a more in-depth answer to this question. 8) What is the difference between CyclicBarrier and CountDownLatch in Java? (answer) Though both CyclicBarrier and CountDownLatch wait for a number of threads on one or more events, the main difference between them is that you can not re-use CountDownLatch once the count reaches to zero, but you can reuse the same CyclicBarrier even after the barrier is broken. See this answer for a few more points and a sample code example.

LeetCode

leetcode.com › discuss › interview-question › operating-system › 4582744 › Multi-Thread-Programming-and-OS

Multi Thread Programming and OS - Discuss - LeetCode

January 17, 2024 - There are two main problems that usually happen on dealing with multi thread programming : 1- Race condition: - when we do not protect the resource with any

LeetCode

leetcode.com › problems › fizz-buzz-multithreaded

Fizz Buzz Multithreaded - LeetCode

Fizz Buzz Multithreaded - You have the four functions: * printFizz that prints the word "fizz" to the console, * printBuzz that prints the word "buzz" to the console, * printFizzBuzz that prints the word "fizzbuzz" to the console, and * printNumber ...

Java67

java67.com › 2012 › 08 › 5-thread-interview-questions-answers-in.html

Top 12 Java Thread, Concurrency, and Multithreading Interview Questions Answers | Java67

There are basically two ways to solve this problem in Java, One by using the wait and notify method and the other by using BlockingQueue in Java. later is easy to implement and a good choice if you are coding in Java 5. The key points to mention, ...

LeetCode

leetcode.com › discuss › interview-question › 1209950 › multithreading-problem-need-help-to-code-this-problem

Multithreading Problem | Need help to code this problem - Discuss - LeetCode

May 15, 2021 - Problem statement: Write a Java program that simulates a Water manufacturing factory. Your factory has infinitely capable Hydrogen and Oxygen producer units (i

LeetCode

leetcode.com › problem-list › concurrency

Problem List - LeetCode

Level up your coding skills and quickly land a job. This is the best place to expand your knowledge and get prepared for your next interview.

Stack Overflow

stackoverflow.com › questions › 78226701 › leetcode-1116-java-concurrency-issue-will-waiting-thread-revisit-code-before

wait - LeetCode 1116 Java Concurrency Issue, will waiting thread revisit code before? - Stack Overflow

Once there's sufficient detail to answer, vote to reopen the question. Closed last year. ... Here is my code for the problem which works fine, however, when I change the while statement right under synchronized statement, it seems any thread that get the lock after notifyall() just continue to run the code and causing odd method accept even number, even method accept odd number. class ZeroEvenOdd { private int n; private AtomicInteger counter; private AtomicInteger mode; private Object lock; public ZeroEvenOdd(int n) { this.n = n; this.counter = new AtomicInteger(0); this.mode = new AtomicInte

LeetCode

leetcode.com › problems › single-threaded-cpu

Single-Threaded CPU - LeetCode

Single-Threaded CPU - You are given n tasks labeled from 0 to n - 1 represented by a 2D integer array tasks, where tasks[i] = [enqueueTimei, processingTimei] means that the i th task will be available to process at enqueueTimei and will take ...

InterviewBit

interviewbit.com › multithreading-interview-questions

Top Java Multithreading Interview Questions (2025) - Interviewbit

One cannot reuse the same CountDownLatch once the count reaches 0. Inter-thread communication, as the name suggests, is a process or mechanism using which multiple threads can communicate with each other. It is especially used to avoid thread polling in java and can be obtained using wait(), notify(), and notifyAll() methods.