Sanden Interview Questions and Answers

Q1. Explain the difference between ArrayList and LinkedList in Java. When would you choose one over the other?
Ans. 
ArrayList uses dynamic arrays, while LinkedList uses doubly linked nodes for storage and access.
• ArrayList provides fast random access (O(1)) due to its underlying array structure.

• LinkedList allows for efficient insertions and deletions (O(1)) at both ends and in the middle.

• ArrayList has a fixed size, requiring resizing (O(n)) when capacity is exceeded, while LinkedList grows dynamically.

• Example: Use ArrayList for frequ...read more
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Q2. What are the advantages and disadvantages of using Java’s synchronized keyword for thread synchronization? Can you explain how the ReentrantLock compares to synchronized?
Ans. 
Java's synchronized keyword offers thread safety but has limitations compared to ReentrantLock.
• Advantages of synchronized: Simple to use and understand.

• Disadvantages of synchronized: Can lead to thread contention and performance issues.

• ReentrantLock allows more flexibility, such as tryLock() and timed lock attempts.

• ReentrantLock can be used for fair locking, preventing thread starvation.

• Synchronized blocks are tied to ...read more
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Q3. What is the difference between == and .equals() in Java? When should each be used, and what issues can arise from improper usage?
Ans. 
In Java, '==' checks reference equality, while '.equals()' checks value equality. Use them appropriately to avoid bugs.
• == compares object references, checking if both point to the same memory location.

• Example: String a = new String('test'); String b = new String('test'); a == b returns false.

• .equals() compares the actual content of the objects.

• Example: a.equals(b) returns true because the content is the same.

• Use '==' f...read more
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Q4. How does the Java garbage collector work? Can you describe the different types of garbage collection algorithms available in Java?
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Q5. What are the main features of Java 8? Can you explain how lambdas and the Stream API have changed the way Java applications are written?
Ans. 
Java 8 introduced lambdas, Stream API, and other features that enhance functional programming and simplify code.
• Lambdas: Enable concise representation of functional interfaces. Example: (x, y) -> x + y.

• Stream API: Facilitates functional-style operations on collections. Example: list.stream().filter(x -> x > 10).collect(Collectors.toList()).

• Default Methods: Allow adding new methods to interfaces without breakin...read more
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Q6. Describe the differences between checked and unchecked exceptions in Java. Provide examples and explain how to handle them properly.
Ans. 
Checked exceptions must be declared or handled, while unchecked exceptions do not require explicit handling.
• Checked exceptions are subclasses of Exception but not of RuntimeException.

• Example: IOException, SQLException are checked exceptions.

• Unchecked exceptions are subclasses of RuntimeException.

• Example: NullPointerException, ArrayIndexOutOfBoundsException are unchecked exceptions.

• Checked exceptions must be caught or d...read more
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Q7. What is the Java Memory Model, and how does it affect multithreading and synchronization? How does volatile help ensure memory visibility?
Ans. 
The Java Memory Model defines how threads interact through memory, ensuring visibility and ordering of shared variables.
• The Java Memory Model (JMM) specifies how threads interact with memory, ensuring consistency and visibility.

• It defines rules for visibility, atomicity, and ordering of operations in a multithreaded environment.

• Synchronization mechanisms (like synchronized blocks) ensure that only one thread can access...read more
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Q8. Can you explain the difference between method overloading and method overriding in Java? Provide examples where each should be used.
Ans. 
Method overloading allows multiple methods with the same name but different parameters; overriding redefines a method in a subclass.
• Method Overloading: Same method name, different parameters (type, number, or both).

• Example of Overloading: 'void add(int a, int b)' and 'void add(double a, double b)'.

• Use Overloading for convenience and readability when methods perform similar functions.

• Method Overriding: Redefining a meth...read more
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Round duration - 90 Minutes
Round difficulty - Medium

This is a written round on paper for everyone. Three coding questions were given. Two out of three must be correct covering every single edge case to qualify for the next round. Only the most optimal solution was to be considered.

Q1. 
Maximum Subarray Sum Problem Statement
Given an array ARR consisting of N integers, your goal is to determine the maximum possible sum of a non-empty contiguous subarray within this array.
Example of Sub...read more
Ans. 
Find the maximum sum of a contiguous subarray in an array of integers.
• Use Kadane's algorithm to find the maximum subarray sum in linear time.

• Initialize two variables: maxSum and currentSum.

• Iterate through the array and update currentSum by adding the current element or starting a new subarray.

• Update maxSum if currentSum becomes greater than maxSum.

• Return maxSum as the maximum subarray sum.
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Round duration - 50 Minutes
Round difficulty - Easy

This was face to face interview round.

Q1. 
Finding Triplets in a Binary Tree Problem Statement
You are given a Binary Tree of integers and an integer 'X'. Your task is to find all the triplets in the tree whose sum is strictly greater than 'X'. Th...read more
Ans. 
Find all triplets in a binary tree whose sum is greater than a given integer X, with a grandparent-parent-child relationship.
• Traverse the binary tree to find all possible triplets.

• Check if the sum of each triplet is greater than X.

• Ensure the relationship of grandparent-parent-child in each triplet.

• Return the valid triplets in any order.

• Handle constraints and edge cases appropriately.
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Round duration - 60 Minutes
Round difficulty - Easy

FACE TO FACE ROUND INTERVIEW

Q1. Can you tell me about yourself?
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Q2. What is the difference between Mutex and Semaphores? Please provide a real-life example.
Ans. 
Mutex is used for exclusive access to a resource by only one thread at a time, while Semaphores can allow multiple threads to access a resource simultaneously.
• Mutex is binary and allows only one thread to access a resource at a time, while Semaphores can have a count greater than one.

• Mutex is used for protecting critical sections of code, while Semaphores can be used for controlling access to a pool of resources.

• Exampl...read more
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Round duration - 60 minutes
Round difficulty - Easy

There was 2 coding questions
Based on ds and algorithms

Q1. 
Minimum Number of Platforms Problem
Your task is to determine the minimum number of platforms required at a railway station so that no train has to wait.
Explanation:
Given two arrays:
• AT - represent...read more
Ans. 
Determine the minimum number of platforms needed at a railway station so that no train has to wait.
• Sort the arrival and departure times arrays in ascending order.

• Initialize two pointers, one for arrival times and one for departure times.

• Increment the platform count when a train arrives and decrement when it departs.

• Keep track of the maximum platform count needed.

• Return the maximum platform count as the minimum number o
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Q2. 
Minimum Number of Swaps to Achieve K-Periodic String
Given a string S of length N, an array A of length M consisting of lowercase letters, and a positive integer K, determine the minimum number of swaps r...read more
Ans. 
The minimum number of swaps required to make a string K-periodic by replacing characters with elements from an array.
• Iterate through the string and check if each character matches the character K positions ahead.

• Count the number of characters that need to be swapped to make the string K-periodic.

• Use the array elements to swap characters in the string.

• Return the total number of swaps needed for each test case.
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Round duration - 45 minutes
Round difficulty - Medium

It was good round they asked me about all the ds and algo basics 
With 2 problems by sharing the screeen

Q1. 
Number of Islands Problem Statement
You are provided with a 2-dimensional matrix having N rows and M columns, containing only 1s (land) and 0s (water). Your goal is to determine the number of islands in t...read more
Ans. 
Count the number of islands in a 2D matrix of 1s and 0s.
• Use Depth First Search (DFS) or Breadth First Search (BFS) to traverse the matrix and identify connected groups of 1s.

• Maintain a visited array to keep track of visited cells to avoid redundant traversal.

• Increment the island count each time a new island is encountered.

• Consider all eight possible directions for connectivity while traversing the matrix.

• Handle edge ca...read more
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Q2. 
Longest Increasing Subsequence Problem Statement
Given an array of integers with 'N' elements, determine the length of the longest subsequence where each element is greater than the previous element. This...read more
Ans. 
Find the length of the longest strictly increasing subsequence in an array of integers.
• Use dynamic programming to solve this problem efficiently.

• Initialize an array to store the length of the longest increasing subsequence ending at each index.

• Iterate through the array and update the length of the longest increasing subsequence for each element.

• Return the maximum value in the array as the result.
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Round duration - 50 minutes
Round difficulty - Medium

In this round, three questions were asked and all of them were based on DSA and a little bit about projects.

Q1. 
Minimum Jumps Problem Statement
Bob and his wife are in the famous 'Arcade' mall in the city of Berland. This mall has a unique way of moving between shops using trampolines. Each shop is laid out in a st...read more
Ans. 
Find the minimum number of jumps Bob needs to make from shop 0 to reach the final shop, or return -1 if impossible.
• Use BFS to traverse through the shops and keep track of the minimum jumps required.

• If at any point the current shop is unreachable (Arr[i] = 0), return -1.

• Optimize by using a visited array to avoid revisiting the same shop.
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Round duration - 25 Minutes
Round difficulty - Medium

Very friendly interviewer. Although waiting time was very high

Q1. 
Pair Sum Problem Statement
You are given an integer array 'ARR' of size 'N' and an integer 'S'. Your task is to find and return a list of all pairs of elements where each sum of a pair equals 'S'.
Note:
...read more
Ans. 
Find pairs of elements in an array that sum up to a given value, sorted in a specific order.
• Iterate through the array and for each element, check if the complement (S - current element) exists in a hash set.

• If the complement exists, add the pair to the result list.

• Sort the result list based on the criteria mentioned in the question.

• Return the sorted list of pairs.
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