Lam Research Sdet (Software Development Engineer in Test) Interview Questions and Answers

Maths, reasoning, puzzles

Dsa, algorithms, trees

Q1. Only basic questions asked
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Q2. Question on dsa
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Q1. Python interview questions
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Round duration - 60 minutes
Round difficulty - Medium

Standard Data Structures and Algorithms round . One has to be fairly comfortable in solving algorithmic problems to pass this round with ease.

Q1. Print all pairs with given sum
You have been given an integer array/list(arr) and a number 'Sum'. Find and return the total number of pairs in the array/list which when added, results equal to the ...read more
Ans. 
Naive Solution :
 
A simple solution is to traverse each element and check if there’s another number in the array which can be added to it to give sum.

TC : O(n^2)
SC : O(1)


Efficient Solution (Using Hashing ) :

We create an empty hash table. Now we traverse through the array and check for pairs in the hash table. If a matching element is found, we print the pair number of times equal to the number of occurrences of the...read more
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Q2. Minimum number of jumps to reach end
You have been given an array 'ARR' of ‘N’ integers. You have to find the minimum number of jumps needed to reach the last index of the array i.e ‘N - 1’ if at a...read more
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Approach 1 : Naive Recursive Approach

A naive approach is to start from the first element and recursively call for all the elements reachable from first element. The minimum number of jumps to reach end from first can be calculated using minimum number of jumps needed to reach end from the elements reachable from first.

minJumps(start, end) = Min ( minJumps(k, end) ) for all k reachable from start

TC : O(n^n)
SC : O(n)


Appr...read more
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Round duration - 70 minutes
Round difficulty - Medium

This round was preety intense and went for over 1 hour . I was asked 2 preety good coding questions (one was from Graphs and the other one was from DP) . After that I was grilled on my Computer Networks and Operating System concepts but luckily I was able to answer all the questions and the interviewer was also quite impressed.

Q1. Two Teams (Check whether graph is bipartite or not)
You are given an undirected graph of ‘N’ nodes and ‘M’ edges. Your task is to print 1 if this graph can be divided into exactly two disjoint cliques. Els...read more
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Algorithm :

1) Create a graph such that there is a edge between each pair of enemies.

2) We need to find that the above graph is bipartite or not. Check whether the graph is 2-colorable or not

3) We can do that by running dfs and using an auxilary array col to store the assigned col of the node.

4) If we can color the graph with two color such that no two enemies have same color then only we can create two teams.


TC : O(V+E...read more
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Q2. Pair Chain - Maximum Length
You are given ‘N’ pairs of integers in which the first number is always smaller than the second number i.e in pair (a,b) -> a < b always. Now we define a pair chain as th...read more
Ans. 
Approach 1 (Using DP ) :

Observe that , If a chain of length k ends at some pairs[i], and pairs[i][1] < pairs[j][0], we can extend this chain to a chain of length k+1

Steps :

1) Sort the pairs by first coordinate, and let dp[i] be the length of the longest chain ending at pairs[i].

2) When i < j and pairs[i][1] < pairs[j][0], we can extend the chain, and so we have the candidate answer dp[j] = max(dp[j], dp[i] + 1...read more
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Q3. Computer Network Question
Explain TCP/IP Protocol
Ans. 
1) TCP or TCP/IP is the Transmission Control Protocol/Internet Protocol.

2) It is a set of rules that decides how a computer connects to the Internet and how to transmit the data over the network.

3) It creates a virtual network when more than one computer is connected to the network and uses the three ways handshake model to establish the connection which makes it more reliable.
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Q4. Computer Network Question
Explain DHCP Protocol
Ans. 
1) DHCP is the Dynamic Host Configuration Protocol.

2) It is an application layer protocol used to auto-configure devices on IP networks enabling them to use the TCP and UDP-based protocols.

3) The DHCP servers auto-assign the IPs and other network configurations to the devices individually which enables them to communicate over the IP network.

4) It helps to get the subnet mask, IP address and helps to resolve the DNS. I
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Q5. Operating System Question
What is meant by Multitasking and Multithreading in OS?
Ans. 
Multitasking : It refers to the process in which a CPU happens to execute multiple tasks at any given time. CPU switching occurs very often when multitasking between various tasks. This way, the users get to collaborate with every program together at the same time. Since it involves rapid CPU switching, it requires some time. It is because switching from one user to another might need some resources. The processes in m...read more
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Round duration - 60 minutes
Round difficulty - Hard

This round majorly focused on past projects and experiences from my Resume and some standard System Design + LLD questions + some basic OOPS questions which a SDE-2 is expected to know .

Q1. System Design Question
Design Pastebin
Ans. 
Approach :

Pastebin allows users to store text-based data over the internet for a set period of time and generate a unique URL corresponding uploaded data to share that with anyone. Users who create that data, can also modify it by logging in to the same account.

Database Schema :

i) users(userID, name, createdAT, metaData)
ii) paste(pasteID, content, URL, createdAt, expiryAt)

Algorithm :

1) create_paste(api_key, content, ex...read more
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Q2. OOPS Question
What is Data Abstraction and how to achive it ?
Ans. 
1) Data abstraction is a very important feature of OOPs that allows displaying only the important information and hiding the implementation details.

2) For example, while riding a bike, you know that if you raise the accelerator, the speed will increase, but you don’t know how it actually happens.

3) This is data abstraction as the implementation details are hidden from the rider.

Data abstraction can be achieved through:

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Q3. OOPS Question
What is Diamond Problem in C++ and how do we fix it?
Ans. 
The Diamond Problem : The Diamond Problem occurs when a child class inherits from two parent classes who both share a common grandparent class i.e., when two superclasses of a class have a common base class.

Solving the Diamond Problem in C++ : The solution to the diamond problem is to use the virtual keyword. We make the two parent classes (who inherit from the same grandparent class) into virtual classes in order to a...read more
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Q4. OOPS Question
What are Friend Functions in C++?
Ans. 
1) Friend functions of the class are granted permission to access private and protected members of the class in C++. They are defined globally outside the class scope. Friend functions are not member functions of the class.

2) A friend function is a function that is declared outside a class but is capable of accessing the private and protected members of the class.

3) There could be situations in programming wherein we w...read more
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Round duration - 90 Minutes
Round difficulty - Medium

DS, ALgo & Operating systems.

Q1. OS Question
What is a race condition?
Ans. 
Took an example of a transaction, explained how the results can be different based on the order of execution of the instructions.
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Q2. OS Question
Difference between mutex and semaphore?
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Very important question, asked a lot in interviews.
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Q3. Power of Two
You have been given an integer 'N'. Your task is to return true if it is a power of two. Otherwise, return false.
An integer 'N' is a power of two, if it can be expressed as ...read more
Ans. 
I started with a while loop kind of program. The interviewer tried to run some corner cases as well but
my code was correct. So he asked me to optimize it further since it was taking O(logn). Then he made me write binary values for 4,8,12 and after that, he said can u deduce some logic from this? Then I
found the correct logic. He was very happy with this.
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Round duration - 100 Minutes
Round difficulty - Medium

Focus on projects, Computer Architecture.

Round duration - 30 Minutes
Round difficulty - Easy