Photomath SDE-2 Interview Questions and Answers

Round duration - 30 minutes
Round difficulty - Medium

Q1. 
Remove Consecutive Duplicates Problem Statement
Given a string S, your task is to recursively remove all consecutive duplicate characters from the string.
Input:
String S
Output:
Output string
Constr...read more
Ans. 
Recursively remove consecutive duplicate characters from a string.
• Use recursion to check if the current character is the same as the next character, if so, skip the next character

• Base case: if the string is empty or has only one character, return the string

• Recursive case: if the current character is the same as the next character, call the function recursively with the string excluding the next character
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Round duration - 90 minutes
Round difficulty - Easy

Q1. 
Reverse String Operations Problem Statement
You are provided with a string S and an array of integers A of size M. Your task is to perform M operations on the string as specified by the indices in array A...read more
Ans. 
Perform a series of reverse string operations on a given string based on specified indices.
• Iterate through the array of indices and reverse the substring of the string based on the given indices.

• Ensure to reverse the substring from the starting index to len(S) - starting index - 1.

• Continue the operations in the sequence specified by the array of indices to get the final string.
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Round duration - 50 minutes
Round difficulty - Medium

Round duration - 60 minutes
Round difficulty - Easy

It is online round and it was conducted around 11 AM on campus. Difficulty was medium. 2 coding questions were asked. One question is based on arrays(easy) and the other question is based on usage of oops concepts like Inheritance, polymorphism. Everything went smooth.

Q1. 
Subarray With Given Sum Problem Statement
Given an array ARR of N integers and an integer S, determine if there exists a contiguous subarray within the array with a sum equal to S. If such a subarray exis...read more
Ans. 
Given an array of integers, find a subarray with a given sum S.
• Use a sliding window approach to find the subarray with the given sum.

• Keep track of the current sum and adjust the window based on the sum.

• Return the start and end indices of the subarray if found, otherwise return [-1, -1].
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Round duration - 50 minutes
Round difficulty - Medium

Round started with self introduction and discussion of project. Everything went fine.
Note: we didn't have hr round due to time constraint. You can expect hr round.

Q1. 
Find the Duplicate Number Problem Statement
Given an integer array 'ARR' of size 'N' containing numbers from 0 to (N - 2). Each number appears at least once, and there is one number that appears twice. Yo...read more
Ans. 
Find the duplicate number in an array of integers from 0 to (N-2).
• Iterate through the array and keep track of the frequency of each number using a hashmap.

• Return the number with a frequency greater than 1 as the duplicate number.
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Q2. Can you explain the concept of normalization and its types?
Ans. 
Normalization is the process of organizing data in a database to reduce redundancy and improve data integrity.
• Normalization is used to eliminate data redundancy and ensure data integrity in a database.

• There are different normal forms such as 1NF, 2NF, 3NF, BCNF, and 4NF.

• Each normal form has specific rules that must be followed to ensure data is properly organized.

• Normalization helps in reducing data anomalies and incon...read more
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Q3. Can you explain the ACID properties in the context of database management systems?
Ans. 
ACID properties are essential characteristics of a transaction in a database management system.
• Atomicity ensures that either all operations in a transaction are completed successfully or none of them are.

• Consistency ensures that the database remains in a valid state before and after the transaction.

• Isolation ensures that the execution of multiple transactions concurrently does not interfere with each other.

• Durability e...read more
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Q4. Can you explain the concepts of Object-Oriented Programming (OOP) with real-life examples?
Ans. 
OOP is a programming paradigm based on the concept of objects, which can contain data and code to manipulate that data.
• OOP focuses on creating objects that interact with each other to solve complex problems.

• Encapsulation: Objects can hide their internal state and require interactions through well-defined interfaces. Example: A car object with methods like start(), stop(), accelerate().

• Inheritance: Objects can inherit a...read more
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Round duration - 360 minutes
Round difficulty - Hard

Timing- Any 6 hours of my choice in the 24 hour window. (10:00 p.m. to 4:00 a.m. I selected)
Environment was very friendly and easy to use.
No significant activity.
This was the only coding round.

Q1. 
Prime Time Again Problem Statement
You are given two integers DAY_HOURS and PARTS. The integer 'DAY_HOURS' represents the number of hours in a day, and the day can be divided into 'PARTS' equal parts. You...read more
Ans. 
Find total instances of equivalent prime groups in a day divided into equal parts.
• Iterate through each part of the day and check for prime pairs in different parts

• Use a helper function to check if a number is prime

• Ensure the day is evenly divided by parts and each prime group has hours from different parts
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Round duration - 10-15 minutes
Round difficulty - Easy

Timing- 12:15 p.m. 
Environment was very good .
Not any significant activity.
The interviewer was very friendly and talked like friends.

Round duration - 20 minutes
Round difficulty - Medium

Timing- 12:30 p.m. to 12:45 p.m
Environment was very comfortable.
No other significant activity.
Interviewer was very good and talking very politely & friendly.

Round duration - 60 mins
Round difficulty - Medium

3 Questions were asked : 2- Trees and 1- Stack.
Interviewer was not receptive at all, I think this was a stress interview.

Q1. 
Validate Binary Search Tree Problem Statement
Given a binary tree with 'N' nodes, determine if it is a Binary Search Tree (BST). Return true if the tree is a BST, otherwise return false.
Example:
Input:
...read more
Ans. 
Validate if a given binary tree is a Binary Search Tree (BST) or not.
• Check if the left subtree of a node contains only nodes with values less than the node's value.

• Check if the right subtree of a node contains only nodes with values greater than the node's value.

• Ensure that both the left and right subtrees are also binary search trees.

• Traverse the tree in-order and check if the elements are in sorted order.

• Use a recurs...read more
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Q2. 
Binary Tree Conversion to Greater Tree
Given a binary tree with 'N' nodes, transform it into a Greater Tree. In this transformation, each node's value should be updated to the sum of its original value and...read more
Ans. 
Convert a binary tree into a Greater Tree by updating each node's value to the sum of its original value and the values of all nodes greater than or equal to it.
• Traverse the tree in reverse inorder (right, root, left) to update the nodes' values.

• Keep track of the sum of nodes visited so far to update each node's value.

• Recursively update the node's value by adding the sum of greater nodes to it.
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Q3. 
Check for Valid Parentheses
You are given a string STR containing only the characters "{", "}", "(", ")", "[", and "]". Your task is to determine if the parentheses in the string are balanced.
Input:
Th...read more
Ans. 
Check if the given string containing only parentheses is balanced or not.
• Use a stack to keep track of opening parentheses.

• Iterate through the string and push opening parentheses onto the stack.

• When a closing parenthesis is encountered, pop from the stack and check if it matches the corresponding opening parenthesis.

• If at the end the stack is empty, return 'YES' else return 'NO'.
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Round duration - 60 mins
Round difficulty - Hard

2 Coding Questions were asked, both were of Medium to Hard Difficulty.

Q1. 
Flatten Multi-Level Linked List
You are given a multi-level linked list containing 'N' nodes. Each node has 'next' and 'child' pointers that may or may not point to other nodes. Your task is to flatten th...read more
Ans. 
Flatten a multi-level linked list into a single linked list by rearranging the pointers.
• Traverse the linked list and whenever a node has a child, flatten the child list and append it after the current node.

• Update the 'next' and 'child' pointers accordingly while flattening the list.

• Continue this process until all nodes are rearranged into a single linked list.
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Q2. 
Rain Water Trapping Problem Statement
Given an array/list ARR of size N, representing an elevation map where each element ARR[i] denotes the elevation of the i-th bar. Your task is to calculate and print ...read more
Ans. 
Calculate the total amount of rainwater that can be trapped between given elevations in an elevation map.
• Use two-pointer approach to keep track of left and right boundaries.

• Calculate the trapped water by finding the minimum of left_max and right_max for each bar.

• Subtract the current bar's height from the minimum of left_max and right_max to get the trapped water.

• Keep updating the left_max and right_max as you iterate t...read more
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Round duration - 90 minutes
Round difficulty - Medium

Timing : It was late night.
How the interviewer was? He was very tired and I had to lead the discussion.
1 System Design Question was asked, had to provide - HLD, LLD, APIs.

Round duration - 60 minutes
Round difficulty - Medium

Timing : Afternoon
How was the environment? Home
Interviewer : Hiring Manager

Q1. Hiring Manager Discussion
Discussed about past Projects, challenges faced, disagreements with manager, why looking for job switch,  leadership principle questions were asked.
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Round duration - 60 minutes
Round difficulty - Medium

Timing - Afternoon
How was the environment? Home
How the interviewer was? Very Helpful Interviewer
Bar raiser Round - Coding + System Design + Leadership principle

Diameter of a binary tree and bfs and dfs questions

Data structure and algorithms

Q1. System design questions
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Round duration - 180 minutes
Round difficulty - Hard

Timing: 8 a.m. to 11a.m.
Environment was optimum.
No significant activity.

Q1. 
Edit Distance Problem Statement
Given two strings S and T with lengths N and M respectively, your task is to find the "Edit Distance" between these strings.
The Edit Distance is defined as the minimum nu...read more
Ans. 
The task is to find the minimum number of operations required to convert one string into another using delete, replace, and insert operations.
• Use dynamic programming to solve the problem efficiently.

• Create a 2D array to store the minimum edit distance for substrings of the two input strings.

• Iterate through the strings and update the array based on the operations needed for each character.

• Return the value in the bottom ...read more
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Round duration - 30 minutes
Round difficulty - Medium

Timing: 12:00 p.m. to 12:30 p.m.
The environment was quite good.
No significant activity.
Interviewers were very friendly. They were behaving like friends.

Round duration - 15 minutes
Round difficulty - Easy

Timing: 3:00 p.m. to 3:20 p.m.
Environment was very good.
No significant activity was monitored.
HR was very good and friendly.

Round duration - 30 minutes
Round difficulty - Medium

It was in the morning about 10:00AM-10:40AM. The platform used for this round was hackerrank. There are 15 MCQ's which cover portions of Aptitude, Data Structures, DBMS, SQL

Q1. 
Minimum Operations Problem Statement
You are given an array 'ARR' of size 'N' consisting of positive integers. Your task is to determine the minimum number of operations required to make all elements in t...read more
Ans. 
Minimum number of operations to make all elements in the array equal by performing addition, subtraction, multiplication, or division.
• Iterate through the array to find the maximum and minimum values.

• Calculate the difference between the maximum and minimum values.

• The minimum number of operations needed is the difference between the maximum and minimum values.
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Round duration - 15 minutes
Round difficulty - Easy

It was in the night around 7:00PM-7:20PM. Platform used for this round was skype. Interviewer was very serious while taking my interview.

Round duration - 90 minutes
Round difficulty - Easy

I got a call from an Amazon recruiter regarding the schedule of the test . She sent me the coding test link which I had to complete within a week. we can attempt the online test anytime, when we have time for a period of 90 minutes at a stretch.Once I completed the test, I got a call to schedule the interviews in two weeks.

Q1. 
Shopping Options Problem Statement
Given arrays representing the costs of pants, shirts, shoes, and skirts, and a budget amount 'X', determine the total number of valid combinations that can be purchased ...read more
Ans. 
Determine total number of valid shopping combinations within budget
• Iterate through all possible combinations of items from each array

• Check if the total cost of the combination is within the budget

• Return the count of valid combinations
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Q2. 
Max Submatrix Problem Statement
You are provided with a matrix MAT consisting of integers, with dimensions N x M (i.e., N rows and M columns). Your objective is to determine the maximum sum submatrix with...read more
Ans. 
Find the maximum sum submatrix in a given matrix.
• Iterate over all possible submatrices and calculate their sums

• Use Kadane's algorithm to find the maximum sum subarray in each row

• Combine the sums of rows to find the maximum sum submatrix
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Round duration - 60 minutes
Round difficulty - Medium

Virtual interview occured in amazon chime.The interviewer gave his introduction, asked me a bit on the kind of projects I’ve worked on. Then he started with a data structure problem.

Q1. 
Clone a Binary Tree with Random Pointers
Given a binary tree where each node has pointers to its left, right, and a random node, create a deep copy of the binary tree.
Input:
The first line contains an ...read more
Ans. 
Clone a binary tree with random pointers and verify if cloning was successful by printing inorder traversal.
• Create a deep copy of the binary tree with random pointers.

• Print the inorder traversal of the cloned binary tree.

• Verify cloning success by printing '1' if successful, '0' otherwise.
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Q2. 
The Ninja Port Problem
Ninja is in a city with 'N' colonies, where each colony contains 'K' houses. He starts at house number "sourceHouse" in colony number "sourceColony" and wants to reach house number ...read more
Ans. 
The Ninja Port Problem involves finding the minimum time for a ninja to travel between colonies and houses using secret paths and teleportation.
• Calculate the minimum time considering teleportation within colonies, traveling between colonies, and secret paths.

• Keep track of the number of secret paths used and ensure they are one-way.

• Consider the constraints provided to optimize the solution.

• Example: N=2, K=3, S=1, P=1, s...read more
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Round duration - 75 Minutes
Round difficulty - Easy

This was taken by an engineering manager who asked me regarding my projects for around 10-15 mins and then we moved to a system design problem. He asked me to design Slack messenger.
I started by listing the functional and non-functional requirements(on which he questioned me a bit), then I moved to draw the high-level architecture. The components which I drew were the clients, gateway service(LB + authentication, etc), Messaging Service, User Service, Web Socket Manager service, Fan Out service(I added this for the group messages thing, but he didn’t interrogate much on that).

He asked me what would be the schema of my messages table and the scenarios in which the recipient user is online/offline.Also asked about the partitioning key and primary key of the 2-3 tables which I had made

Round duration - 60 minutes
Round difficulty - Hard

BarRaiser Round

This was again taken by an engineering manager who discussed my projects in depth for around 20-25 mins. In the remaining time he asked me 2 dsa questions. (Yes I too was surprised that he didn’t ask anything regarding design).

In almost all the rounds, I was asked questions related to Amazon Leadership principles, so do make sure you go through those before sitting for the interview process. You can refer to this link(https://www.codingninjas.com/codestudio/problem-lists/top-amazon-coding-interview-questions) for practicing the same, I found it useful. 
In the design rounds, interviewer doesn’t expect the most ideal answer from you and unless your choice of technology is outrageously wrong, he won’t pinpoint that.

Q1. 
Group Anagrams Together
Given an array/list of strings STR_LIST, group the anagrams together and return each group as a list of strings. Each group must contain strings that are anagrams of each other.
E...read more
Ans. 
Group anagrams together in a list of strings.
• Iterate through the list of strings and sort each string to group anagrams together.

• Use a hashmap to store the sorted string as key and the original string as value.

• Return the values of the hashmap as the grouped anagrams.
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Q2. 
Add Two Numbers Represented by Linked Lists
Your task is to find the sum list of two numbers represented by linked lists and return the head of the sum list.
Explanation:
The sum list should be a linked...read more
Ans. 
Add two numbers represented by linked lists and return the head of the sum list.
• Traverse both linked lists simultaneously while keeping track of carry from previous sum

• Create a new linked list to store the sum of the two numbers

• Handle cases where one linked list is longer than the other by padding with zeros

• Update the sum and carry values accordingly while iterating through the linked lists
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