Classplus React Js Frontend Developer Interview Questions and Answers

DS/ALGO and problem-solving was asked in round one

Round duration - 60 Minutes
Round difficulty - Easy

4 Questions which were of Easy, Medium, and Hard level.

Q1. 
Lowest Common Ancestor of a Binary Tree III
The structure of a binary tree has been modified so that each node includes a reference to its parent node.
Problem Statement
You are provided with two nodes,...read more
Ans. 
This question is about finding the lowest common ancestor of two nodes in a binary tree with parent references.
• Traverse from the given nodes to their respective root nodes and store the paths in two separate lists.

• Compare the two lists and find the last common node.

• Return the last common node as the lowest common ancestor.
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Q2. 
Maximum Subarray Problem Statement
Ninja has been given an array, and he wants to find a subarray such that the sum of all elements in the subarray is maximum.
A subarray 'A' is considered greater than a...read more
Ans. 
The problem is to find a subarray with the maximum sum in a given array.
• Iterate through the array and keep track of the maximum sum and the current sum.

• If the current sum becomes negative, reset it to 0.

• Update the maximum sum if the current sum is greater.

• Also keep track of the start and end indices of the subarray with the maximum sum.

• Return the subarray using the start and end indices.
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Round duration - 50 Minutes
Round difficulty - Easy

Q1. 
Next Greater Element Problem Statement
Given a list of integers of size N, your task is to determine the Next Greater Element (NGE) for every element. The Next Greater Element for an element X is the firs...read more
Ans. 
The task is to find the next greater element for each element in an array.
• Iterate through the array from right to left.

• Use a stack to keep track of the elements that have a greater element to their right.

• For each element, pop elements from the stack until a greater element is found or the stack is empty.

• If a greater element is found, it is the next greater element for the current element.

• If the stack becomes empty, the...read more
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Q2. 
Trapping Rain Water Problem Statement
You are given a long type array/list ARR of size N, representing an elevation map. The value ARR[i] denotes the elevation of the ith bar. Your task is to determine th...read more
Ans. 
The question asks to find the total amount of rainwater that can be trapped in the given elevation map.
• Iterate through the array and find the maximum height on the left and right side of each bar.

• Calculate the amount of water that can be trapped at each bar by taking the minimum of the maximum heights on both sides and subtracting the height of the bar.

• Sum up the amount of water trapped at each bar to get the total amo
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Round duration - 30 Minutes
Round difficulty - Easy

It is just a formality round, asked basic questions like relocation and joining date etc

Round duration - 60 Minutes
Round difficulty - Easy

Q1. 
0/1 Knapsack Problem Statement
A thief is planning to rob a store and can carry a maximum weight of 'W' in his knapsack. The store contains 'N' items where the ith item has a weight of 'wi' and a value of...read more
Ans. 
Yes, the 0/1 Knapsack problem can be solved using dynamic programming with a space complexity of not more than O(W).
• Use a 1D array to store the maximum value that can be stolen for each weight capacity from 0 to W.

• Iterate through each item and update the array based on whether including the item would increase the total value.

• The final value in the array at index W will be the maximum value that can be stolen.
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Q2. 
Find the Second Largest Element
Given an array or list of integers 'ARR', identify the second largest element in 'ARR'.
If a second largest element does not exist, return -1.
Example:
Input:
ARR = [2,...read more
Ans. 
Find the second largest element in an array of integers.
• Iterate through the array to find the largest and second largest elements.

• Handle cases where all elements are identical.

• Return -1 if a second largest element does not exist.
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Round duration - 60 Minutes
Round difficulty - Easy

System Design Round

Q1. Design a system for Twitter, discussing its architecture, key components, and scalability considerations.
Ans. 
Design a scalable system for Twitter with key components and architecture.
• Use microservices architecture for scalability and fault isolation.

• Key components include user service, tweet service, timeline service, and notification service.

• Use a distributed database like Cassandra for storing tweets and user data.

• Implement a message queue like Kafka for handling real-time updates and notifications.

• Use a caching layer like ...read more
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Round duration - 30 Minutes
Round difficulty - Easy

It is just a formality

Round duration - 120 Minutes
Round difficulty - Medium

Machine Coding Round
2 Hours in Total
15 Mins for Question Explaination and Doubts
1.5 Hours for coding
15 mins to discuss the approach 

Timing - 3 to 5 pm (They are flexible)
Interviewer was very patient and helped me understand the question

Round duration - 60 Minutes
Round difficulty - Medium

2 Data Strucutre Questions
Timing 5-6 pm (They are flexible)
Google Meet
Online IDE

Q1. 
Unique Binary Search Trees Problem Statement
Given an integer 'N', your task is to compute the number of structurally unique BSTs (binary search trees) that can be formed using an exact number of 'N' uniq...read more
Ans. 
The task is to compute the number of structurally unique BSTs that can be formed using an exact number of unique values.
• Use dynamic programming to solve the problem efficiently.

• The number of structurally unique BSTs can be calculated using Catalan numbers.

• For N nodes, the number of structurally unique BSTs is given by the Nth Catalan number.

• Example: For N=3, the number of structurally unique BSTs is 5.
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Q2. 
Subsequences of String Problem Statement
You are provided with a string 'STR' that consists of lowercase English letters ranging from 'a' to 'z'. Your task is to determine all non-empty possible subsequen...read more
Ans. 
Generate all possible subsequences of a given string.
• Use recursion to generate all possible subsequences by including or excluding each character in the string.

• Maintain a current index to keep track of the characters being considered.

• Append the current character to each subsequence generated so far.

• Recursively call the function with the next index to include or exclude the next character.

• Base case: When the current ind...read more
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Round duration - 60 Minutes
Round difficulty - Easy

HIRING MANAGER ROUND

Discussion about the organisation now questions

Round duration - 90 Minutes
Round difficulty - Medium

1 easy and 2 medium-hard DSA problems to solve

Q1. 
Hurdle Game Problem Statement
Kevin is playing a hurdle game where he must jump over hurdles to clear levels. Each level ‘i’ consists of ‘i’ hurdles (e.g., Level 6 has 6 hurdles).
Given the total number ...read more
Ans. 
Given the total number of hurdles Kevin has jumped, determine how many levels he has cleared.
• Iterate through levels while subtracting hurdles from total jumped until remaining hurdles are less than current level

• Return the current level as the number of levels cleared
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Q2. 
N Queens Problem
Given an integer N, find all possible placements of N queens on an N x N chessboard such that no two queens threaten each other.
Explanation:
A queen can attack another queen if they ar...read more
Ans. 
The N Queens Problem involves finding all possible placements of N queens on an N x N chessboard without threatening each other.
• Use backtracking algorithm to explore all possible configurations.

• Keep track of rows, columns, and diagonals to ensure queens do not threaten each other.

• Generate valid configurations recursively and backtrack when a solution is not possible.
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Q3. 
Count Ways To Travel Triangular Pyramid
Bob is given a triangular pyramid with vertices 'O', 'X', 'Y', and 'Z'. He is also provided with an integer 'N'. Bob can move to any adjacent vertex in a single ste...read more
Ans. 
Calculate the number of ways Bob can complete a journey in a triangular pyramid after N steps.
• Bob can move to any adjacent vertex in a single step

• Bob must return to vertex 'O' after exactly 'N' steps

• Calculate the number of different ways Bob can complete the journey

• Return the result modulo 1000000007

• Consider the constraints provided
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Round duration - 60 Minutes
Round difficulty - Medium

2 DSA problems and computer subject questions

Q1. 
Generate Binary Strings with No Consecutive 1s
Given an integer K, your task is to produce all binary strings of length 'K' that do not contain consecutive '1's.
Input:
The input begins with an integer ...read more
Ans. 
Generate all binary strings of length 'K' with no consecutive '1's in lexicographically increasing order.
• Use backtracking to generate all possible binary strings of length 'K' with no consecutive '1's.

• Start with an empty string and recursively add '0' or '1' based on the condition of no consecutive '1's.

• Sort the generated strings in lexicographically increasing order before outputting them.
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Q2. 
Shuffle Two Strings Problem Statement
You are provided with three strings A, B, and C. The task is to determine if C is formed by interleaving A and B. C is considered an interleaving of A and B if:
• T...read more
Ans. 
Check if a string is formed by interleaving two other strings.
• Iterate through characters of A, B, and C simultaneously to check if C is formed by interleaving A and B.

• Use dynamic programming to efficiently solve the problem.

• Handle edge cases like empty strings or unequal lengths of A, B, and C.

• Example: A = 'aab', B = 'abc', C = 'aaabbc' should return True.
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Round duration - 60 Minutes
Round difficulty - Easy

DSA round

Q1. 
Ninja and Intersection of Lines
You are given coordinates for two lines on a 2D plane: Line 'AB' is defined by points 'A' and 'B', and Line 'PQ' is defined by points 'P' and 'Q'. Your task is to find the ...read more
Ans. 
Find the intersection point of two lines on a 2D plane given their coordinates.
• Calculate the slopes of both lines using the given coordinates.

• Use the slope-intercept form of a line to find the equations of the two lines.

• Solve the equations simultaneously to find the intersection point.

• Return the coordinates of the intersection point with precision up to 6 decimal places.
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Q2. 
Cycle Detection in Directed Graph
Determine if a given directed graph contains a cycle. If the graph has at least one cycle, return true. Otherwise, return false.
Input:
The first line of input contains...read more
Ans. 
Detect cycles in a directed graph and return true if a cycle exists, false otherwise.
• Use Depth First Search (DFS) to detect cycles in the directed graph.

• Maintain a visited array to keep track of visited vertices and a recursion stack to detect back edges.

• If a vertex is visited and is present in the recursion stack, then a cycle exists.

• Example: For the input 4 4, the graph has a cycle 0 -> 1 -> 2 -> 3 -> 1.
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Round duration - 30 Minutes
Round difficulty - Easy

It is a managerial round

Q1. How does a URL work and what is a load balancer?
Ans. 
A URL is a web address that specifies the location of a resource on the internet. A load balancer distributes incoming network traffic across multiple servers to ensure optimal resource utilization and prevent overload.
• A URL (Uniform Resource Locator) is a reference to a web resource that specifies its location on a computer network and the mechanism for retrieving it.

• URLs typically consist of a protocol (such as HTTP ...read more
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