Owler Interview Questions and Answers

Round duration - 150 Minutes
Round difficulty - Medium

It was an Aptitude test and Technical objective test of 60 minutes followed by a Coding test of 90 minutes.There was a 1 hour gap b/w the two tests.

Q1. 
Count Derangements
Determine the number of derangements possible for a set of 'N' elements. A derangement is a permutation where no element appears in its original position.
Input:
An integer 'T' repres...read more
Ans. 
Count the number of derangements possible for a set of 'N' elements.
• Derangement is a permutation where no element appears in its original position.

• Use dynamic programming to calculate derangements efficiently.

• Apply the formula: D(n) = (n-1) * (D(n-1) + D(n-2)), with base cases D(1) = 0 and D(2) = 1.
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Q2. 
Prime Numbers Identification
Given a positive integer N, your task is to identify all prime numbers less than or equal to N.
Explanation:
A prime number is a natural number greater than 1 that has no po...read more
Ans. 
Identify all prime numbers less than or equal to a given positive integer N.
• Iterate from 2 to N and check if each number is prime

• Use the Sieve of Eratosthenes algorithm for better efficiency

• Optimize by only checking up to the square root of N for divisors
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Q3. 
Common Elements Problem Statement
Identify and output the common strings present in both given arrays of lowercase alphabets for each test case.
Input:
The first line contains an integer 'T' representin...read more
Ans. 
The problem requires identifying and outputting common strings present in two arrays of lowercase alphabets for each test case.
• Iterate through the elements of the second array and check if they are present in the first array.

• Use a hash set or map to efficiently check for common elements.

• Return the common strings in the order they appear in the second array.
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Round duration - 60 Minutes
Round difficulty - Medium

This round had 1 question from DSA particulary Trees and after that some questions from OOPS were asked.

Q1. 
Spiral Order Traversal of a Binary Tree
Given a binary tree with N nodes, your task is to output the Spiral Order traversal of the binary tree.
Input:
The input consists of a single line containing elem...read more
Ans. 
Implement a function to return the spiral order traversal of a binary tree.
• Traverse the binary tree level by level, alternating the direction of traversal.

• Use a queue to keep track of nodes at each level.

• Append nodes to the result list based on the traversal direction.

• Handle null nodes appropriately to maintain the spiral order.

• Example: Input: 1 2 3 -1 -1 4 5, Output: 1 3 2 4 5
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Q2. What is the difference between an Abstract Class and an Interface in Java?
Ans. 
Abstract class can have both abstract and non-abstract methods, while interface can only have abstract methods.
• Abstract class can have constructor, fields, and methods, while interface can only have constants and abstract methods.

• A class can extend only one abstract class, but can implement multiple interfaces.

• Abstract classes are used to provide a common base for subclasses, while interfaces are used to define a contr...read more
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Q3. What is the static keyword in Java?
Ans. 
The static keyword in Java is used to create class-level variables and methods that can be accessed without creating an instance of the class.
• Static variables are shared among all instances of a class.

• Static methods can be called without creating an object of the class.

• Static blocks are used to initialize static variables.

• Example: public static int count = 0;
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Q4. What is the difference between a constructor and a method in Object-Oriented Programming?
Ans. 
Constructor is a special method used to initialize objects, while a method is a regular function that performs a specific task.
• Constructors are called automatically when an object is created, while methods need to be called explicitly.

• Constructors have the same name as the class, while methods have unique names.

• Constructors do not have a return type, while methods have a return type.

• Example: Constructor - public ClassN...read more
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Round duration - 60 minutes
Round difficulty - Medium

This round had 2 questions from DSA and after that some basic HR questions were asked.

Q1. 
Ways To Make Coin Change
Given an infinite supply of coins of varying denominations, determine the total number of ways to make change for a specified value using these coins. If it's not possible to make...read more
Ans. 
The task is to find the total number of ways to make change for a specified value using given denominations.
• Use dynamic programming to solve this problem efficiently.

• Create a 1D array to store the number of ways to make change for each value from 0 to the target value.

• Iterate through the denominations and update the array based on the current denomination.

• The final answer will be the value at the target index of the ar
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Q2. 
Palindrome String Validation
Determine if a given string 'S' is a palindrome, considering only alphanumeric characters and ignoring spaces and symbols.
Note:
The string 'S' should be evaluated in a case...read more
Ans. 
Check if a given string is a palindrome after removing special characters, spaces, and converting to lowercase.
• Remove special characters and spaces from the input string

• Convert the string to lowercase

• Check if the modified string is a palindrome by comparing characters from start and end
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