MagicPin Senior Java Developer Interview Questions and Answers

Round duration - 60 Minutes
Round difficulty - Medium

This round was purely based on Data Structures and Algorithms . One has to be fairly comfortable in solving Algorithmic problems to pass this round . Both the questions asked were quite common and luckily I had already prepared them from CodeStudio and LeetCode.

Q1. 
Binary Tree Traversals Problem Statement
Given a Binary Tree with 'N' nodes, where each node holds an integer value, your task is to compute the In-Order, Pre-Order, and Post-Order traversals of the binar...read more
Ans. 
Compute the In-Order, Pre-Order, and Post-Order traversals of a Binary Tree given in level-order format.
• Implement functions to perform In-Order, Pre-Order, and Post-Order traversals of a Binary Tree.

• Use level-order input to construct the Binary Tree.

• Traverse the Binary Tree recursively to generate the required traversals.

• Ensure proper handling of null nodes represented by -1 in the input.

• Return the three traversals as
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Q2. 
Reverse Linked List Problem Statement
Given a Singly Linked List of integers, your task is to reverse the Linked List by altering the links between the nodes.
Input:
The first line of input is an intege...read more
Ans. 
Reverse a singly linked list by altering the links between nodes.
• Iterate through the linked list and reverse the links between nodes

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

• Update the links between nodes to reverse the list

• Return the head of the reversed linked list
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Round duration - 45 Minutes
Round difficulty - Medium

This round basically tested some concepts from Data Structures and File Manipulation .

Q1. 
Intersection of Two Arrays Problem Statement
Given two arrays A and B with sizes N and M respectively, both sorted in non-decreasing order, determine their intersection.
The intersection of two arrays in...read more
Ans. 
The problem involves finding the intersection of two sorted arrays efficiently.
• Use two pointers to iterate through both arrays simultaneously.

• Compare elements at the pointers and move the pointers accordingly.

• Handle cases where elements are equal and update the intersection array.

• Return the intersection array as the result.
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Round duration - 90 minutes
Round difficulty - Medium

It was in the morning, where there were 3 questions to answer.

Q1. 
Number of Islands Problem Statement
You are provided with a 2-dimensional matrix having N rows and M columns, containing only 1s (land) and 0s (water). Your goal is to determine the number of islands in t...read more
Ans. 
Count the number of islands in a 2D matrix of 1s and 0s.
• Use Depth First Search (DFS) or Breadth First Search (BFS) to traverse the matrix and identify connected groups of 1s.

• Maintain a visited array to keep track of visited cells to avoid redundant traversal.

• Increment the island count each time a new island is encountered.

• Consider all eight possible directions for connectivity while traversing the matrix.

• Handle edge ca...read more
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Q2. 
Missing Numbers Problem Statement
You are provided with an array called ARR, consisting of distinct positive integers. Your task is to identify all the numbers that fall within the range of the smallest a...read more
Ans. 
Identify missing numbers within the range of smallest and largest elements in an array.
• Find the smallest and largest elements in the array.

• Generate a list of numbers within this range.

• Filter out the numbers present in the array.

• Return the missing numbers in sorted order.
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Q3. 
Count Leaf Nodes in a Binary Tree
Given a binary tree, your task is to count and return the number of leaf nodes present in it.
A binary tree is a data structure where each node has at most two children,...read more
Ans. 
Count and return the number of leaf nodes in a binary tree.
• Traverse the binary tree and count nodes with both left and right children as NULL.

• Use recursion to traverse the tree efficiently.

• Leaf nodes have no children, so check for NULL left and right children to identify them.
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Round duration - 20 minutes
Round difficulty - Medium

It was a system design round.

Q1. Can you describe the system design of the OLA app?
Ans. 
OLA app system design involves multiple components like user interface, driver matching algorithm, payment processing, etc.
• User interface for booking rides and tracking

• Driver matching algorithm based on location and availability

• Payment processing for seamless transactions

• Real-time tracking of rides for both users and drivers
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Round duration - 45 minutes
Round difficulty - Medium

It was a DS Algo round.

Q1. 
Diagonal Traversal of a Binary Tree Problem Statement
Given a binary tree, your task is to determine the diagonal traversal of the tree.
Example:
Input:
1 2 3 4 -1 5 6 -1 7 -1 -1 -1 -1 -1 -1
Output:
...read more
Ans. 
Diagonal traversal of a binary tree involves traversing nodes diagonally from top to bottom and left to right.
• Traverse the tree level by level, starting from the root node.

• For each level, keep track of the diagonal nodes and their children.

• Use a queue to store nodes at each level and traverse them accordingly.

• Example: For input 1 2 3 4 -1 5 6 -1 7 -1 -1 -1 -1 -1 -1, the diagonal traversal is 1 3 6 2 5 4 7.
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Q2. 
Minimum Number Of Taps To Water Garden Problem Statement
You are required to determine the minimum number of taps that need to be opened to water an entire one-dimensional garden defined along the x-axis,...read more
Ans. 
Find the minimum number of taps to water an entire garden along the x-axis.
• Iterate over the taps and find the farthest point each tap can reach.

• Sort the taps based on their starting points and use a greedy approach to select the taps.

• Keep track of the farthest point reachable by the selected taps and the number of taps opened.

• Return the minimum number of taps needed to water the entire garden or -1 if it's impossible.
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Round duration - 15 minutes
Round difficulty - Medium

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