60+ Amazon Software Engineer Interview Questions and Answers

Reverse a singly linked list of integers.

• Iterate through the linked list and reverse the pointers to point to the previous node instead of the next node.

• Keep track of the current, previous, and next nodes while traversing the list.

• Update the head of the linked list to be the last node encountered during traversal.

Merge nodes between zeroes in a linked list to store the sum of included nodes.

• Traverse the linked list and keep track of sum between zeroes

• Merge nodes between zeroes by updating the sum in the merged node

• Handle edge cases like empty list or single node between zeroes

• Ensure the list starts and ends with a zero

Reverse a singly linked list of integers and return the head of the reversed linked list.

• Traverse the linked list and reverse the pointers to point to the previous node instead of the next node

• Use three pointers - prev, current, and next to reverse the linked list

• Update the head of the reversed linked list to be the last element of the original linked list

• Example: Input: 1 -> 2 -> 3 -> 4 -> NULL, Output: 4 -> 3 -> 2 -> 1 -> NULL

The task is to find the length of the longest common subsequence between two given strings.

• Use dynamic programming to solve this problem efficiently.

• Create a 2D array to store the lengths of common subsequences of substrings.

• Iterate through the strings to fill the array and find the longest common subsequence.

• Example: For strings 'abcde' and 'ace', the longest common subsequence is 'ace' with a length of 3.

Find the minimum cost to purchase a specific weight of oranges given the cost of different weight packets.

• Iterate through the list of costs and find the minimum cost to achieve the desired weight

• Keep track of the total cost while considering available packet weights

• Return -1 if it is not possible to buy exactly the desired weight

Given 'N' ropes of varying lengths, find the minimum cost to connect all ropes into one single rope.

• Sort the lengths of ropes in ascending order.

• Keep connecting the two shortest ropes at each step.

• Add the cost of connecting the two ropes to the total cost.

• Repeat until all ropes are connected.

• Return the total cost as the minimum cost to connect all ropes.

Suggest a data structure for efficient search of a string in 10 files and print line number and file if string appears more than once.

• Use a hash table to store the file name and line number of each occurrence of the string.

• Iterate through each file and for each line, check if the string is present and update the hash table accordingly.

• Print the hash table entries for the string.

The task is to fill the 'next' field of each node in a binary tree to point to the next node at the same level.

• Use a level order traversal to process the tree nodes.

• Maintain a queue to store the nodes at each level.

• For each node, set its 'next' field to the next node in the queue.

• If a node is the last node at its level, set its 'next' field to NULL.

ArrayList is preferred for frequent retrieval operations due to fast random access, while LinkedList is suitable for frequent insertions/deletions with fast O(1) complexity.

• Use ArrayList for scenarios where frequent retrieval operations are needed, such as searching for elements in a large collection.

• Choose LinkedList when frequent insertions/deletions are required, like maintaining a queue or stack with dynamic size.

• Consider memory overhead and performance trade-offs when de...read more

Given an infinite staircase with a broken kth step, find the maximum height we can reach in n rounds of jumping i steps.

• We can start by jumping the maximum number of steps in each round until we reach the broken step.

• After reaching the broken step, we can discard the i steps that would land us on the broken step and jump the remaining steps.

• We can continue this pattern until we reach the maximum height we can reach without stepping on the broken step.

ReentrantLock should be used instead of synchronized when more flexibility and control over locking mechanisms is required.

• Use ReentrantLock when you need to implement advanced locking mechanisms like tryLock() or lockInterruptibly()

• ReentrantLock supports fair locking, ensuring that threads acquire the lock in the order they requested it

• Explicit unlocking in ReentrantLock can help prevent deadlocks and improve performance in certain scenarios

In Java, == checks for reference equality while equals() checks for value equality. Misuse of == can lead to logical errors.

• Override equals() when you want to compare the actual content of objects in user-defined classes.

• Override hashCode() method alongside equals() to ensure consistent behavior in collections like HashMap.

• Implement Comparable interface and override compareTo() method for natural ordering of objects.

Garbage collection in Java automatically reclaims memory occupied by unused objects using different GC algorithms and memory regions.

• Force garbage collection in Java can be done using System.gc() or Runtime.gc() methods.

• It is generally not recommended to force garbage collection as it can disrupt the JVM's natural memory management process and cause performance issues.

• Forcing garbage collection may not guarantee immediate memory reclamation and can lead to inefficient memory ...read more

Lambda expressions in Java 8 improve readability and maintainability by enabling concise and functional-style programming.

• Lambda expressions allow writing more compact code by reducing boilerplate code.

• They enable passing behavior as arguments to methods, making code more modular and flexible.

• Example: (a, b) -> a + b is a lambda expression that adds two numbers.

To find anagrams of a given word in a dictionary, use a hash table to store sorted versions of each word as keys and their corresponding original words as values.

• Create a hash table to store the anagrams

• Iterate through each word in the dictionary

• Sort the characters of the word and use it as a key in the hash table

• If the key already exists, add the word to the list of values for that key

• Print the list of values for the given word's sorted characters

Find the nearest greater value of a given value in a Binary Search Tree (BST).

• Start from the root node and compare the given value with the current node's value.

• If the given value is less than the current node's value, move to the left subtree.

• If the given value is greater than the current node's value, move to the right subtree.

• Keep track of the closest greater value encountered while traversing the tree.

• Return the closest greater value found.

ArrayList and LinkedList are both classes in Java that implement the List interface, but they have different underlying data structures.

• ArrayList uses a dynamic array to store elements, providing fast random access but slower insertion and deletion.

• LinkedList uses a doubly linked list to store elements, providing fast insertion and deletion but slower random access.

• Choose ArrayList when you need fast random access and know the size of the list beforehand. Choose LinkedList wh...read more

Java Stream is a sequence of elements that supports functional-style operations. It differs from Iterator by being more declarative and allowing for parallel processing.

• Java Stream is a high-level abstraction over collections that allows for functional-style operations like map, filter, reduce, etc.

• Streams are more declarative compared to Iterators, which are imperative. This means that with Streams, you specify what you want to do rather than how to do it.

• Streams can be used...read more

Immutability in Java means objects cannot be modified after creation. String class achieves immutability by not allowing changes to its value.

• Immutability means once an object is created, its state cannot be changed.

• String class in Java is immutable because its value cannot be modified once it is assigned.

• Advantages of immutable objects include thread safety, security, and ease of caching.

final, finally, and finalize have different meanings in Java.

• final is a keyword used to restrict the user from changing the value of a variable, making it a constant.

• finally is a block of code that is always executed, whether an exception is thrown or not.

• finalize is a method used for cleanup operations before an object is garbage collected.

Singleton design pattern ensures a class has only one instance and provides a global point of access to it.

• Create a private static instance of the class within the class itself.

• Provide a public static method to access the instance, creating it if necessary.

• Make the constructor private to prevent instantiation from outside the class.

• Use synchronized keyword or double-checked locking to ensure thread safety.

Method overloading is when multiple methods have the same name but different parameters, while method overriding is when a subclass provides a specific implementation of a method in its superclass.

• Method overloading is achieved within the same class by having multiple methods with the same name but different parameters.

• Method overriding occurs in a subclass that provides a specific implementation of a method that is already provided by its superclass.

• Method overloading is use...read more

Java annotations are metadata that provide data about a program but do not affect the program itself. They are used in frameworks like Spring to configure and customize behavior.

• Java annotations are used to provide metadata about classes, methods, fields, etc. in a program.

• In frameworks like Spring, annotations are used to configure various aspects of the application, such as dependency injection, transaction management, and request mapping.

• Built-in annotations in Java includ...read more

Using Java's synchronized keyword for thread synchronization has advantages like simplicity and disadvantages like potential for deadlock. ReentrantLock offers more flexibility and control.

• Advantages of synchronized keyword: simplicity, built-in support in Java

• Disadvantages of synchronized keyword: potential for deadlock, lack of flexibility

• ReentrantLock advantages: more flexibility, ability to try and lock with timeout

• ReentrantLock disadvantages: more verbose syntax, need to...read more

Java garbage collector manages memory by automatically deallocating memory that is no longer in use.

• Java garbage collector runs in the background and identifies objects that are no longer reachable by the application.

• It uses different algorithms like Mark-Sweep, Mark-Compact, and Copying to reclaim memory.

• Mark-Sweep algorithm identifies and marks objects for deletion, then sweeps through and deallocates them.

• Mark-Compact algorithm moves reachable objects to one end of the mem...read more

The Java Memory Model defines how threads interact through memory and how synchronization ensures visibility and consistency.

• Java Memory Model specifies how threads interact with memory

• Synchronization ensures visibility and consistency of shared data among threads

• Volatile keyword ensures changes made by one thread are immediately visible to other threads

• Example: Using volatile keyword to share a boolean flag among multiple threads

Java Streams can handle parallel processing using parallel streams. Pitfalls include increased complexity and potential for race conditions.

• Java Streams can be processed in parallel by calling the parallel() method on a stream.

• Potential pitfalls of using parallel streams include increased complexity, potential for race conditions, and performance overhead due to thread management.

• To mitigate these pitfalls, ensure that the operations performed on the stream are stateless and ...read more

In Java, == compares memory addresses while .equals() compares the actual values of objects.

• Use == to compare primitive data types or to check if two objects reference the same memory location.

• Use .equals() to compare the actual values of objects, especially for String comparisons.

• Improper usage can lead to unexpected results, such as comparing objects instead of their values.

Java 8 introduced features like lambdas and Stream API which have revolutionized the way Java applications are written.

• Lambdas allow for more concise and readable code by enabling functional programming style.

• Stream API provides a way to process collections of objects in a functional way, allowing for easier parallel processing and improved performance.

• Java 8 also introduced default methods in interfaces, allowing for backward compatibility with existing code.

• The new Date and...read more

Functional interfaces in Java are interfaces with a single abstract method. They can be used with lambda expressions for functional programming.

• Functional interfaces have only one abstract method, but can have multiple default or static methods.

• Lambda expressions can be used to implement the abstract method of a functional interface concisely.

• An example of a custom functional interface is 'Calculator' with a single abstract method 'calculate'.

Checked exceptions must be handled at compile time, while unchecked exceptions do not need to be caught or declared.

• Checked exceptions are subclasses of Exception class, while unchecked exceptions are subclasses of RuntimeException class.

• Checked exceptions must be caught or declared in the method signature using 'throws', while unchecked exceptions do not have this requirement.

• Examples of checked exceptions include IOException and ClassNotFoundException, while examples of unc...read more

ACID properties in DBMS ensure data integrity and consistency in transactions.

• Atomicity: All operations in a transaction are completed successfully or none at all.

• Consistency: Data remains consistent before and after the transaction.

• Isolation: Transactions are isolated from each other until they are completed.

• Durability: Once a transaction is committed, changes are permanent and survive system failures.

Function to check if a string of parenthesis is balanced

• Use a stack to keep track of opening parenthesis

• If a closing parenthesis is encountered, pop from stack and check if it matches

• If stack is empty and a closing parenthesis is encountered, return False

• If all parenthesis are matched and stack is empty, return True

Count the occurrences of words in a paragraph.

• Split the paragraph into words using whitespace as a delimiter.

• Create a dictionary to store the count of each word.

• Iterate through the words and increment the count in the dictionary.

• Return the dictionary with the word counts.

Find common elements out of two sorted array

• Use two pointers to traverse both arrays simultaneously

• Compare elements at each pointer and move the pointer of the smaller element

• If elements are equal, add to common elements list and move both pointers

• Stop when either pointer reaches end of array

Find the element that is repeated once in an array where all elements are repeated twice

• Iterate through the array and use a hashmap to keep track of the count of each element

• Once the iteration is complete, check the hashmap for the element with a count of 1

Use a combination of sliding window and hashmap to find top k most visited website patterns by users

• Parse the csv file to extract user and website data

• Use a sliding window to generate all possible website patterns for each user

• Use a hashmap to count the frequency of each website pattern

• Sort the website patterns based on frequency and return the top k patterns

Boundary traversal of a tree is the process of visiting the nodes on the boundary of a tree in a specific order.

• The boundary traversal can be done in three steps: left boundary, leaf nodes, and right boundary.

• For the left boundary, start from the root and traverse down the left side of the tree until reaching a leaf node.

• For the leaf nodes, perform an inorder traversal to visit all the leaf nodes of the tree.

• For the right boundary, start from the rightmost leaf node and trave...read more

Convert a Binary Search Tree to a Doubly Linked List.

• Create a DLL node class with left, right, and data fields.

• Traverse the BST in-order and add each node to the DLL.

• Adjust the left and right pointers of each node to create the DLL.

• Return the head of the DLL.

Create a package dependency diagram based on object-oriented design principles.

• Identify the main classes/modules in the system

• Determine the relationships between classes/modules (e.g. inheritance, composition, aggregation)

• Visualize the dependencies between classes/modules using arrows or lines

• Consider using UML diagrams to represent the package dependency

The question is about balanced parenthesis and finding the maximum units on a truck.

• To check if a string of brackets is balanced, we can use a stack data structure.

• To find the maximum units on a truck, we need to sort the items by weight and then start adding them to the truck until it reaches its maximum capacity.

A question about finding nodes at a distance of K from a given node in a graph.

• Use BFS or DFS to traverse the graph and keep track of the distance from the starting node.

• Maintain a visited set to avoid revisiting nodes.

• Return all nodes at distance K from the starting node.

• Example: Find all nodes at distance 2 from node A in a graph.

Linked list is a data structure where each element points to the next element. Operations like insertion, deletion, traversal can be performed on linked lists.

• Linked list is a linear data structure where elements are stored in nodes. Each node contains data and a reference to the next node.

• Operations on linked list include insertion, deletion, traversal, and searching.

• For example, to insert a new node at the beginning of a linked list, create a new node with the data and poin...read more

Graph problems and popular algo implementations

• Shortest Path: Dijkstra's, Bellman-Ford, Floyd-Warshall

• Minimum Spanning Tree: Prim's, Kruskal's

• Topological Sorting: Kahn's, DFS

• Max Flow: Ford-Fulkerson, Edmonds-Karp

• Travelling Salesman Problem: Held-Karp, Christofides

• Graph Coloring: Greedy, Backtracking

Detect if a binary tree is symmetric.

• Check if the left and right subtrees are mirror images of each other.

• Use a recursive approach to compare corresponding nodes.

• Base case: if both nodes are null, return true.

• If one node is null and the other is not, return false.

• If the values of the nodes are not equal, return false.

• Recursively check if the left subtree of the left node is symmetric to the right subtree of the right node.

• Recursively check if the right subtree of the left nod...read more

The question is about advanced data structures and algorithms for a senior software engineer role.

• Focus on advanced data structures like AVL trees, B-trees, and tries

• Discuss complex algorithms like Dijkstra's algorithm, A* search algorithm, and dynamic programming

• Highlight experience with optimizing time and space complexity

• Provide examples of solving challenging coding problems or implementing complex algorithms

Find the maximum diagonal sum of a binary tree

• Traverse the tree diagonally and keep track of the sum at each diagonal level

• Use a hashmap to store the sum at each diagonal level

• Return the maximum sum from the hashmap

Finding the merge point of two linked lists.

• Traverse both linked lists to find their lengths.

• Move the pointer of the longer list ahead by the difference in lengths.

• Iterate both lists simultaneously until the merge point is found.

Traversing a linked list involves iterating through each node starting from the head until the end is reached.

• Start at the head node

• Iterate through each node by following the 'next' pointer until the end is reached

• Perform desired operations on each node as needed

DP + Sliding window problem

• Dynamic Programming (DP) is a technique to solve optimization problems by breaking them down into smaller subproblems

• Sliding window is a technique to solve problems by maintaining a window of elements in an array or string

• Combining DP and sliding window can be useful in solving problems that require both techniques

Treasury Island can be found using Depth First Search on a 2D array of strings.

• Implement a Depth First Search algorithm to traverse the 2D array of strings

• Start from a specific point on the island and explore all possible paths

• Keep track of visited cells to avoid infinite loops

• Return the path that leads to the treasury on the island

Recursively sum the values of nodes in a binary tree

• Use a recursive function to traverse the tree and add the values of each node

• Base case: if the current node is null, return 0

• Recursive step: return the sum of current node value, left subtree sum, and right subtree sum

Designing Amazon involves creating a user-friendly e-commerce platform with a vast product selection, efficient search and recommendation algorithms, secure payment processing, and reliable delivery logistics.

• Develop a user-friendly interface for easy navigation and product search

• Implement recommendation algorithms based on user behavior and preferences

• Integrate secure payment processing systems to protect customer information

• Establish efficient delivery logistics for timely ...read more

To invert a binary search tree (BST), swap the left and right children of each node recursively.

• Start from the root node and recursively swap the left and right children of each node.

• Repeat this process for all nodes in the BST.

• The final result will be the inverted BST.

Create a classic minesweeper game with a grid of cells to uncover without hitting any mines.

• Create a grid of cells with hidden mines randomly placed

• Allow the player to uncover cells and reveal numbers indicating nearby mines

• Implement logic to end the game if a mine is uncovered or all non-mine cells are revealed

Reverse a linked list

• Iterate through the linked list and change the direction of the pointers

• Use three pointers to keep track of current, previous and next nodes

• Recursively reverse the linked list

Count the number of islands in a 2D grid where '1' represents land and '0' represents water.

• Iterate through the grid and for each '1' encountered, perform a depth-first search to mark all adjacent '1's as visited.

• Increment the island count for each new island found.

• Ensure to handle boundary conditions and visited cells properly to avoid infinite loops.

Sorting linked lists involves rearranging the nodes in a specific order.

• Use a sorting algorithm such as merge sort or quick sort to rearrange the nodes in the linked list.

• Iterate through the linked list and compare each node with the next one to determine the correct order.

• Consider the time complexity of the sorting algorithm to ensure efficient sorting of the linked list.

Designing a bus transit system involves planning routes, schedules, stops, and ticketing systems.

• Consider the population density and traffic patterns of the area to determine the number and frequency of bus routes.

• Create a network of bus stops strategically located near residential areas, commercial centers, and transportation hubs.

• Implement a reliable ticketing system that allows for cashless payments and offers options for daily, weekly, and monthly passes.

• Integrate real-ti...read more

Subsequences of arrays are all possible combinations of elements in an array.

• A subsequence can be of any length, including 0 and the entire array.

• The order of elements in a subsequence must be maintained.

• The number of possible subsequences of an array of length n is 2^n.

• For example, the subsequences of [1, 2, 3] are [], [1], [2], [3], [1, 2], [1, 3], [2, 3], [1, 2, 3].

To troubleshoot a problem, identify the issue, gather information, analyze data, and implement a solution.

• Identify the problem by asking questions and gathering information

• Analyze data to determine the root cause of the problem

• Implement a solution by testing and verifying the fix

• Document the problem and solution for future reference