Amazon Senior Engineer Interview Questions and Answers

Round duration - 90 minutes
Round difficulty - Hard

This was an online coding round where we were supposed to solve 2 questions under 90 minutes . Both the questions in my set were related to Graphs and were quite tricky and heavy to implement.

Q1. 
Path Counting in Directed Graph
Given a directed graph with a specified number of vertices V and edges E, your task is to calculate the total number of distinct paths from a given source node S to all ot...read more
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Q2. 
Course Schedule II Problem Statement
You are provided with a number of courses 'N', some of which have prerequisites. There is a matrix named 'PREREQUISITES' of size 'M' x 2. This matrix indicates that fo...read more
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Round duration - 60 Minutes
Round difficulty - Medium

This was a Data Structures and Algorithms round with some standard questions . I was expected to come up with an
efficient approach and code it as well .

Q1. 
Merge Intervals Problem Statement
You are provided with 'N' intervals, each containing two integers denoting the start time and end time of the interval.
Your task is to merge all overlapping intervals a...read more
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Q2. 
Longest Route Problem Statement
Given a 2-dimensional binary matrix called Mat of size N x M that consists solely of 0s and 1s, find the length of the longest path from a specified source cell to a destina...read more
Ans. 
Find the length of the longest path from a source cell to a destination cell in a binary matrix.
• Use depth-first search (DFS) to explore all possible paths from source to destination.

• Keep track of visited cells to avoid revisiting them.

• Return the length of the longest path found, or -1 if no path exists.
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Round duration - 50 Minutes
Round difficulty - Medium

This was also a DSA round where I was asked to code only one of the questions but I eventually ended up coding both
as I had some spare time and explained my approches very smoothly to the interviewer . This round went preety well .

Q1. 
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
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Q2. 
Search In Rotated Sorted Array Problem Statement
Given a rotated sorted array ARR of size 'N' and an integer 'K', determine the index at which 'K' is present in the array.
Note:
1. If 'K' is not present...read more
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Round duration - 50 Minutes
Round difficulty - Medium

This was also a DSA round with 2 questions of Medium to Hard difficulty . I was expected to follow some clean code and OOPS principles to write the code in this round .

Q1. 
Rank from Stream Problem Statement
Given an array of integers ARR and an integer K, determine the rank of the element ARR[K].
Explanation:
The rank of any element in ARR is defined as the number of elem...read more
Ans. 
Determine the rank of an element in an array based on preceding smaller elements.
• The rank of ARR[K] is the count of elements smaller than ARR[K] before index K.

• Example: For ARR = [6, 2, 9, 7] and K = 3, ARR[K] = 7. Elements before it are [6, 2], so rank = 2.

• Iterate through the array from index 0 to K-1 to count smaller elements.

• Consider edge cases: if K = 0, rank is always 0 since there are no elements before it.
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Q2. 
LRU Cache Design Question
Design a data structure for a Least Recently Used (LRU) cache that supports the following operations:
1. get(key) - Return the value of the key if it exists in the cache; otherw...read more
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Round duration - 60 Minutes
Round difficulty - Medium

This was a Data Structures and Algorithms round with preety good questions . I was expected to come up with an efficient approach and code it as well .

Q1. 
K Closest Points to Origin Problem Statement
Your house is located at the origin (0,0) of a 2-D plane. There are N neighbors living at different points on the plane. Your goal is to visit exactly K neighb...read more
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Q2. 
Power Set Generation
Given a sorted array of 'N' integers, your task is to generate the power set for this array. Each subset of this power set should be individually sorted.
A power set of a set 'ARR' i...read more
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Round duration - 50 Minutes
Round difficulty - Hard

This was also a DSA round where I was asked to code only one of the questions but I eventually ended up coding both as I had some spare time and explained my approches very smoothly to the interviewer . This round went preety well .

Q1. 
Roman Numeral to Integer Conversion
Convert a string representing a Roman numeral into its integer equivalent and return the result.
Explanation:
Roman numerals are represented by seven different symbol...read more
Ans. 
Convert a Roman numeral string to its integer equivalent.
• Create a mapping of Roman numeral symbols to their integer values.

• Iterate through the input string and add the corresponding integer values.

• Handle cases where subtraction is needed (e.g., IV = 4, IX = 9).
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Q2. 
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
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Round duration - 50 Minutes
Round difficulty - Medium

This was also a DSA round with 2 questions . One was implementation heavy and the other was related to recursion and so I handled it carefully so that my code does not run into TLE or Segmentation Fault.

Q1. 
Arithmetic Expression Evaluation Problem Statement
You are provided with a string expression consisting of characters '+', '-', '*', '/', '(', ')' and digits '0' to '9', representing an arithmetic express...read more
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Q2. 
Remove Duplicates from Sorted Array Problem Statement
You are given a sorted integer array ARR of size N. Your task is to remove the duplicates in such a way that each element appears only once. The outpu...read more
Ans. 
Remove duplicates from a sorted array in-place with O(1) extra memory.
• Use two pointers - one for iterating through the array and another for placing unique elements.

• Compare current element with next element to identify duplicates and skip them.

• Update array in-place by moving unique elements to the front.

• Return the length of the array after removal of duplicates.
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Round duration - 50 Minutes
Round difficulty - Medium

This was a typical System Design round where I was asked about the various features of Facebook and what sort of data structures and algorithms are used in implementing them .

Q1. How does Facebook store likes and dislikes?
Ans. 
Facebook stores likes and dislikes using a combination of databases and algorithms.
• Likes and dislikes are stored in databases such as MySQL or Cassandra.

• Algorithms are used to analyze user behavior and recommend content based on likes and dislikes.

• User interactions with posts, pages, and ads are tracked to determine likes and dislikes.

• Likes and dislikes may also be used to personalize the user's feed and target ads mor...read more
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Q2. How does Facebook implement graph search?
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Round duration - 50 Minutes
Round difficulty - Medium

This was a preety intense round as I was grilled more on my System Design concepts but eventually I was able to asnwers all the questions with some help from the interviewer.

Q1. What is Hadoop and why is it used?
Ans. 
Hadoop is a framework for distributed storage and processing of large data sets.
• Hadoop is used for storing and processing big data across a distributed network of computers.

• It is based on the MapReduce programming model, which allows for parallel processing of data.

• Hadoop consists of HDFS for storage and YARN for resource management.

• It is used for tasks like data warehousing, log processing, recommendation systems, and...read more
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Q2. How does Facebook Chat work?
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Round duration - 60 minutes
Round difficulty - Easy

In first round they asked me 2 coding questions where he asked me to code as close as possible to the actual one.

Q1. 
Ninja and Sorted Array Merging Problem
Ninja is tasked with merging two given sorted integer arrays ARR1 and ARR2 of sizes 'M' and 'N', respectively, such that the merged result is a single sorted array w...read more
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Q2. 
Word Distance Calculation
Given a document represented as an array/list ARR of words with length N, find the smallest distance between two given words for multiple queries. The distance is defined as the ...read more
Ans. 
Calculate the smallest index distance between two words in a document for multiple queries.
• Store indices of each word in a dictionary for quick access.

• For each query, check if both words exist in the document.

• Calculate the minimum distance using the stored indices.

• If a word is missing, return 'N' (length of ARR).

• Example: For ARR = ['hot', 'a', 'b', 'dog'], query ('hot', 'dog') returns 3.
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Round duration - 60 minutes
Round difficulty - Easy

Then in the second round they asked a little about tree and told me to code 2 codes.

Q1. 
Level Order Traversal Problem Statement
Given a binary tree of integers, return the level order traversal of the binary tree.
Input:
The first line contains an integer 'T', representing the number of te...read more
Ans. 
The problem requires implementing a function to return the level order traversal of a binary tree.
• Implement a function that takes the root of the binary tree as input and returns the level order traversal of the tree.

• Use a queue data structure to perform level order traversal.

• Process each level of the tree one by one, starting from the root node.

• Print the node values at each level in the order they appear from left to ...read more
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Q2. 
Combination Sum Problem Statement
Given an array of distinct positive integers ARR and a non-negative integer 'B', find all unique combinations in the array where the sum is equal to 'B'. Numbers can be c...read more
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Round duration - 30 minutes
Round difficulty - Easy

HR round with typical behavioral problems.