Cogencis Information Services Java Developer Interview Questions and Answers

Round duration - 30 minutes
Round difficulty - Medium

This was a MCQ round. 30 ques in 30 mins consisting of difficult quantitative aptitude questions were to be solved.

Round duration - 60 minutes
Round difficulty - Medium

In this test round, 2 coding questions were given. Either write the code or pseudo code

Q1. 
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 all valid configurations and print them out.
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Q2. 
Sort 0 1 2 Problem Statement
Given an integer array arr of size 'N' containing only 0s, 1s, and 2s, write an algorithm to sort the array.
Input:
The first line contains an integer 'T' representing the n...read more
Ans. 
Sort an array of 0s, 1s, and 2s in linear time complexity.
• Use three pointers to keep track of 0s, 1s, and 2s while traversing the array.

• Swap elements based on the values encountered to sort the array in-place.

• Time complexity should be O(N) and space complexity should be O(1).
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Round duration - 60 minutes
Round difficulty - Easy

This was a technical round with questions on DSA.

Q1. 
Reverse Words in a String: Problem Statement
You are given a string of length N. Your task is to reverse the string word by word. The input may contain multiple spaces between words and may have leading o...read more
Ans. 
Reverse words in a string while handling leading, trailing, and multiple spaces.
• Split the input string by spaces to get individual words

• Reverse the order of the words

• Join the reversed words with a single space in between
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Q2. 
Circular Linked List Detection
You are provided with the head of a linked list containing integers. Your task is to determine if the linked list is circular.
Note:
• A linked list is considered circula...read more
Ans. 
Detect if a given linked list is circular by checking if it forms a closed loop.
• Traverse the linked list using two pointers, one moving at double the speed of the other.

• If the two pointers meet at any point, the linked list is circular.

• If the faster pointer reaches the end of the list (NULL), the linked list is not circular.
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Round duration - 30 minutes
Round difficulty - Easy

HR round with typical behavioral problems.

Round duration - 40 minutes
Round difficulty - Easy

Q1. 
Find a Node in Linked List
Given a singly linked list of integers, your task is to implement a function that returns the index/position of an integer value 'N' if it exists in the linked list. Return -1 i...read more
Ans. 
Implement a function to find the index of a given integer in a singly linked list.
• Traverse the linked list while keeping track of the index of each element.

• Compare each element with the target integer 'N'.

• Return the index if 'N' is found, otherwise return -1.

• Handle cases where the list is empty or 'N' is not found.

• Consider the constraints on the number of test cases and the length of the linked list.
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Q2. 
Implement Stack with Linked List
Your task is to implement a Stack data structure using a Singly Linked List.
Explanation:
Create a class named Stack which supports the following operations, each in O(1...read more
Ans. 
Implement a Stack data structure using a Singly Linked List with operations in O(1) time.
• Create a class named Stack with getSize, isEmpty, push, pop, and getTop methods.

• Use a Singly Linked List to store the elements of the stack.

• Ensure each operation runs in constant time complexity (O(1)).

• Handle edge cases like empty stack appropriately.

• Example: For input '5', '3 10', '5', '1', '2', '4', the output should be '10', '1'
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Q3. 
Cycle Detection in a Singly Linked List
Determine if a given singly linked list of integers forms a cycle or not.
A cycle in a linked list occurs when a node's next points back to a previous node in the ...read more
Ans. 
Detect if a singly linked list has a cycle using O(N) time complexity and O(1) space complexity.
• Use Floyd's Tortoise and Hare algorithm to detect cycle in linked list

• Maintain two pointers, slow and fast, moving at different speeds

• If there is a cycle, the two pointers will eventually meet

• If one of the pointers reaches the end of the list (null), there is no cycle
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Round duration - 20 minutes
Round difficulty - Easy

Q1. 
Top View of Binary Tree
Given a binary tree of integers, the task is to return the top view of the given binary tree. The top view of the binary tree is the set of nodes visible when viewed from the top.
...read more
Ans. 
Return the top view of a binary tree given in level-order format.
• Traverse the binary tree in level-order and keep track of the horizontal distance of each node from the root.

• Use a map to store the nodes at each horizontal distance, and only keep the first node encountered at each distance.

• Return the values of the nodes stored in the map in sorted order of their horizontal distance.

• Example: For the given binary tree, th
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Q2. 
Problem Statement: Delete Node In A Linked List
Given a singly linked list of integers and a reference to a node, your task is to delete that specific node from the linked list. Each node in the linked li...read more
Ans. 
Given a singly linked list of integers and a reference to a node, delete the specified node from the linked list.
• Traverse the linked list to find the node to be deleted

• Update the pointers to skip over the node to be deleted

• Print the modified linked list after deletion
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Create a CRUD application

Q1. Javascript, hoisting ,promise ,callback function
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Q2. Array , object ,JSON,for loop
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Q3. Introduction react js,and other frameworks ,like angular, Vue
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Q1. What are your salary expectations?
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Q2. Basic details for joining company
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Q1. Basics questions of react native
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Very basic aptitude questions along with few coding questions

Q1. A problem statement was given and we had to provide an optimal approach to design and handle that problem
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Q2. Oops concepts, SQL queries
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