Pure Storage Member Technical Staff Interview Questions and Answers

Round duration - 120 Minutes
Round difficulty - Medium

This was an online Coding+MCQ round. Both the coding questions were related to DP and were of Medium to Hard Difficulty.The MCQ's were of easy-medium level but one has to be fast in order to complete the section in the given time frame.

Q1. 
Maximum Sum Problem Statement
You are given an array ARR of N integers. Your task is to perform operations on this array until it becomes empty, and maximize the sum of selected elements. In each operatio...read more
Ans. 
Given an array, select elements to maximize sum by removing adjacent elements.
• Iterate through the array and keep track of the count of each element.

• Select the element with the highest count first, then remove adjacent elements.

• Repeat the process until the array is empty and sum the selected elements.
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Q2. 
Longest Common Prime Subsequence Problem Statement
Imagine Ninja is tackling a puzzle during his long summer vacation. He has two arrays of integers, each with lengths 'N' and 'M'. Ninja's task is to dete...read more
Ans. 
Find the length of the longest common prime subsequence between two arrays of integers.
• Iterate through both arrays to find prime numbers

• Use a set to keep track of common prime numbers

• Return the size of the set as the length of the longest common prime subsequence
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Round duration - 60 Minutes
Round difficulty - Medium

This round had 2 Algorithmic questions wherein I was supposed to code both the problems after discussing their approaches and respective time and space complexities . After that , I was grilled on some OOPS concepts related to C++.

Q1. 
Detect and Remove Loop in Linked List
For a given singly linked list, identify if a loop exists and remove it, adjusting the linked list in place. Return the modified linked list.
Expected Complexity:
A...read more
Ans. 
Detect and remove loop in a singly linked list in place with O(n) time complexity and O(1) space complexity.
• Use Floyd's Cycle Detection Algorithm to identify the loop in the linked list.

• Once the loop is detected, use two pointers to find the start of the loop.

• Adjust the pointers to remove the loop and return the modified linked list.
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Q2. 
Stack using Two Queues Problem Statement
Develop a Stack Data Structure to store integer values using two Queues internally.
Your stack implementation should provide these public functions:
Explanation:
...read more
Ans. 
Implement a stack using two queues to store integer values with specified functions.
• Create a stack class with two queue data members.

• Implement push(data), pop(), top(), size(), and isEmpty() functions.

• Use one queue for pushing elements and another for temporary storage during operations.

• Ensure proper handling of edge cases such as empty stack.

• Example: If input is Q = 5, 1 42, 2, 3, 1 17, the output should be 42, -1, 17
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Q3. What are Vtable and VPTR in C++?
Ans. 
Vtable and VPTR are used in C++ for implementing polymorphism through virtual functions.
• Vtable (Virtual Table) is a table of function pointers used to implement dynamic dispatch in C++ for virtual functions.

• VPTR (Virtual Pointer) is a pointer that points to the Vtable of an object, allowing dynamic binding of virtual functions at runtime.

• Vtable is created for each class that has virtual functions, containing pointers t...read more
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Q4. What are friend functions in C++?
Ans. 
Friend functions in C++ are functions that are not members of a class but have access to its private and protected members.
• Friend functions are declared inside a class with the keyword 'friend'.

• They can access private and protected members of the class.

• They are not member functions of the class, but have the same access rights as member functions.

• Example: friend void displayDetails(Student);
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Round duration - 60 minutes
Round difficulty - Medium

This round had 3 preety good questions related to DSA and some questions revolving around Memory Management and Operating Systems.

Q1. 
Predecessor and Successor in Binary Search Tree (BST)
Given a binary search tree (BST) with 'N' nodes, find the predecessor and successor of a given 'KEY' node in the BST.
Explanation:
The predecessor o...read more
Ans. 
Find predecessor and successor of a given node in a binary search tree (BST).
• Predecessor is the node visited just before the given node in an inorder traversal.

• Successor is the node visited immediately after the given node in an inorder traversal.

• Return -1 if predecessor or successor does not exist.

• Implement inorder traversal to find predecessor and successor.
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Q2. 
Count Ways to Reach the N-th Stair Problem Statement
You are provided with a number of stairs, and initially, you are located at the 0th stair. You need to reach the Nth stair, and you can climb one or tw...read more
Ans. 
The problem involves counting the number of distinct ways to climb N stairs by taking 1 or 2 steps at a time.
• Use dynamic programming to solve the problem efficiently.

• The number of ways to reach the Nth stair is the sum of the number of ways to reach the (N-1)th stair and the (N-2)th stair.

• Handle base cases for N=0 and N=1 separately.

• Apply modulo operation to avoid overflow while calculating the result.

• Consider using me...read more
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Q3. 
Good Arrays Problem Statement
You are given an array 'A' of length 'N'. You must choose an element from any index in this array and delete it. After deleting the element, you will obtain a new array of le...read more
Ans. 
Given an array, find the number of 'good' arrays that can be formed by deleting one element.
• Iterate through each element in the array and check if deleting it results in a 'good' array

• Keep track of the sum of elements at odd and even indices to determine if the array is 'good'

• Return the count of 'good' arrays
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Q4. What is memory protection in operating systems?
Ans. 
Memory protection in operating systems prevents one process from accessing or modifying the memory of another process.
• Memory protection ensures that each process has its own isolated memory space.

• It prevents unauthorized access to memory locations, improving system stability and security.

• Operating systems use techniques like virtual memory and access control lists to enforce memory protection.

• Examples include segmentat...read more
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Round duration - 60 minutes
Round difficulty - Easy

Th interviewer asked me questions related to various topics of OS, Data Structures and Algorithm.
Tips: Have a strong hold on topics of OS like segmentation and buddy systems.

Q1. What is segmentation?
Ans. 
Segmentation is the process of dividing a larger entity into smaller parts or segments.
• Segmentation is commonly used in image processing to separate objects of interest from the background.

• It is also used in marketing to divide a target market into smaller groups based on demographics, behavior, or other factors.

• In networking, segmentation refers to dividing a network into smaller subnetworks to improve performance and
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Q2. What are the advantages and disadvantages of the buddy system?
Ans. 
The buddy system has advantages like increased safety and support, but also drawbacks like dependency and lack of independence.
• Advantages: increased safety, support, accountability, motivation

• Disadvantages: dependency, lack of independence, potential for conflicts

• Example: In a buddy system at work, colleagues can support each other in completing tasks and provide motivation to stay on track.

• Example: However, relying to...read more
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Q3. What is a page fault?
Ans. 
A page fault occurs when a program tries to access a page of memory that is not currently in physical RAM.
• Occurs when a program tries to access a page of memory not in physical RAM

• Results in the operating system needing to retrieve the page from disk

• Can lead to a temporary pause in program execution
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Round duration - 60 minutes
Round difficulty - Easy

The round consisted of questions of heap, Towers of hanoi and other questions related to CV.
Tips: Time complexity analysis of Towers of Hanoi Problem is important. Good skillset in DS and Algorithms, Bit Manipulation.

Q1. 
Tower of Hanoi Problem Statement
You have three rods numbered from 1 to 3, and 'N' disks initially stacked on the first rod in increasing order of their sizes (largest disk at the bottom). Your task is to...read more
Ans. 
Tower of Hanoi problem where 'N' disks need to be moved to another rod following specific rules in less than 2^N moves.
• Implement a recursive function to move disks from one rod to another following the rules.

• Use the concept of recursion and backtracking to solve the Tower of Hanoi problem efficiently.

• Maintain a count of moves and track the movement of disks in a 2-D array/list.

• Ensure that larger disks are not placed on...read more
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Q2. 
Convert Array to Min Heap Task
Given an array 'ARR' of integers with 'N' elements, you need to convert it into a min-binary heap.
A min-binary heap is a complete binary tree where each internal node's va...read more
Ans. 
Convert the given array into a min-binary heap by modifying the array elements.
• Iterate through the array and heapify each node starting from the last non-leaf node to the root node.

• For each node, compare it with its children and swap if necessary to satisfy the min-heap property.

• Continue this process until the entire array is converted into a min-heap.
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Round duration - 30 minutes
Round difficulty - Easy

The HR asked about my hobbies, extra curricular activities and checked my personality.