Amazon Lab126 SDE Interview Questions and Answers

Q1. Link list reversal
Ans. 
Reversing a linked list involves changing the direction of the pointers between nodes.
• Initialize three pointers: prev, current, and next.

• Set prev to null and current to the head of the list.

• Iterate through the list: update next to current.next, current.next to prev, then move prev and current forward.

• Continue until current is null, then set the head to prev.

• Example: For list 1 -> 2 -> 3, after reversal it becomes...read more
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Q2. OS all concepts
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Q1. Two-Sum Problem
Ans. 
The Two-Sum Problem involves finding two numbers in an array that add up to a specific target sum.
• Given an array of integers and a target sum, identify two numbers that sum to the target.

• Example: For array [2, 7, 11, 15] and target 9, the answer is indices 0 and 1 (2 + 7 = 9).

• Use a hash map to store numbers and their indices for efficient lookup.

• Time complexity is O(n) with a single pass through the array.
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Round duration - 180 minutes
Round difficulty - Medium

It was a long round of around 3 hours divided into 2 parts 
1. Aptitude(MCQ)
2. Coding(Subjective)

Q1. 
Maximum Meetings Selection
You are tasked with scheduling meetings in a single meeting room. Given N meetings, each with a start time Start[i] and end time End[i], determine the maximum number of meetings...read more
Ans. 
Given start and end times of meetings, find the maximum number of meetings that can be scheduled in a single room.
• Sort the meetings based on their end times in ascending order.

• Iterate through the sorted meetings and select the ones that do not overlap with the previously selected meetings.

• Keep track of the selected meetings and return their indices.
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Q2. 
Partition to K Equal Sum Subsets Problem
Given an array of integers and a positive integer 'K', determine if it is possible to divide the array into 'K' non-empty subsets such that the sum of elements in ...read more
Ans. 
The problem involves dividing an array into K subsets with equal sum.
• Use backtracking to try all possible combinations of subsets.

• Keep track of the sum of elements in each subset and check if they are equal to the target sum.

• Optimize by sorting the array in descending order and assigning elements to subsets greedily.

• Handle edge cases like when the sum of elements is not divisible by K.
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Q3. 
Merge k Sorted Linked Lists
You are provided with 'K' sorted linked lists, each sorted in increasing order. Your task is to merge all these lists into one single sorted linked list and return the head of ...read more
Ans. 
Merge k sorted linked lists into one single sorted linked list.
• Create a min-heap to store the heads of all linked lists.

• Pop the smallest element from the heap and add it to the result list.

• If the popped element has a next element, push it back to the heap.

• Repeat until all elements are merged into a single sorted list.
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Q4. 
Sort a "K" Sorted Doubly Linked List
Given a doubly-linked list with N nodes, where each node’s position deviates at most K positions from its position in the sorted list, your task is to sort this given ...read more
Ans. 
Sort a doubly linked list where each node's position deviates at most K positions from its position in the sorted list.
• Iterate through the doubly linked list and maintain a min-heap of size K+1 to keep track of the next smallest element.

• Remove the smallest element from the heap and add it to the sorted list. Update the heap with the next element from the removed node's next position.

• Continue this process until all node...read more
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Q5. 
Duplicate Subtrees Problem Statement
Given a binary tree, return the root values of all duplicate subtrees. Two subtrees are considered duplicate if they have the same structure with identical node values...read more
Ans. 
Find root values of duplicate subtrees in a binary tree.
• Traverse the tree in a bottom-up manner to identify duplicate subtrees.

• Use a hashmap to store the subtree structures and their frequencies.

• Return the root values of duplicate subtrees based on hashmap entries.
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Round duration - 25 minutes
Round difficulty - Medium

The technical Interview round was not at all difficult. The main focus of the interviewer was my projects and development fields.
He also asked some DS/Algo questions that were at a medium level, and some easy questions for database management.

Q1. Can you explain the concept of keys in database management systems?
Ans. 
Keys in database management systems are unique identifiers for rows in a table.
• Keys ensure data integrity by enforcing uniqueness and relationships between tables.

• Primary key uniquely identifies each record in a table (e.g. employee ID).

• Foreign key establishes a link between two tables by referencing the primary key of another table.
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Round duration - 15 minutes
Round difficulty - Easy

It took place on the same day as the technical round. It was quite the easiest round of all. The interviewer just asked me to introduce myself, projects I have worked on, my Internships experience, and were they internships paid.

Q1. Can you tell me about yourself?
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Q2. Can you tell me about the different projects that you have worked on?
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Q1. 2 string based coding questions RXJS and js based input output questions
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Round duration - 60 minutes
Round difficulty - Medium

Q1. What are functional relations in the context of database management systems (DBMS)?
Ans. 
Functional relations in DBMS define a relationship between input and output values where each input has a unique output.
• Functional relations ensure that each input value maps to only one output value.

• They are commonly used in database design to enforce data integrity and consistency.

• For example, in a table storing employee information, the employee ID can be a functional key that uniquely identifies each employee.
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Round duration - 40 minutes
Round difficulty - Hard

Q1. Puzzle
Questions related to Web development and machine learning
Ans. 
The question is related to Web development and machine learning.
• Web development involves creating websites and web applications using languages like HTML, CSS, and JavaScript.

• Machine learning is a subset of artificial intelligence that involves building models to make predictions based on data.

• Examples of web development frameworks include React, Angular, and Vue.js.

• Examples of machine learning algorithms include linea...read more
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Round duration - 20 minutes
Round difficulty - Medium

Cs subjects regarding OS, C, DBMS

Q1. Implement insertion sort
Ans. 
Insertion sort is a simple sorting algorithm that builds the final sorted array one item at a time.
• Start with the second element and compare it with the first element, swap if necessary

• Move to the third element and compare it with the second and first element, swap if necessary

• Continue this process until the entire array is sorted

• Time complexity: O(n^2)

• Example: ['banana', 'apple', 'orange', 'grape'] -> ['apple', 'banan...read more
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Q2. Implement tree and code
Ans. 
Implementing a tree data structure using code
• Define a Node class with left and right child pointers

• Implement insert, search, and delete functions

• Traversal methods: inorder, preorder, postorder

• Examples: binary search tree, AVL tree, red-black tree
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Q1. DSA ARRAY QUESTIONS EASY TO MEDIUM LEVEL
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