Knoc Door Services Operations Engineer Interview Questions, Process, and Tips

Round duration - 40 minutes
Round difficulty - Medium

Asked about time complexity of algorithm, puzzles, DBMS, cutting edge technologies etc. What are indexes?

Q1. 
Flip Bits Problem Explanation
Given an array of integers ARR of size N, consisting of 0s and 1s, you need to select a sub-array and flip its bits. Your task is to return the maximum count of 1s that can b...read more
Ans. 
Given an array of 0s and 1s, find the maximum count of 1s by flipping a sub-array at most once.
• Iterate through the array and keep track of the maximum count of 1s obtained by flipping a sub-array.

• Consider flipping a sub-array from index i to j and calculate the count of 1s in the resulting array.

• Return the maximum count of 1s obtained by flipping a sub-array at most once.
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Round duration - 20 minutes
Round difficulty - Medium

Asked 1 standard algorithm

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.
• Iterate through the matrix and perform depth-first search (DFS) to find connected 1s.

• Mark visited cells to avoid redundant traversal.

• Increment island count whenever a new island is encountered.
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There were 19 questions consists of aptitude and technical subject. Then 2 codes were there . Then 1 code of SQL query .

Q1. Technical Interview 45min Introduce yourself Projects included in Resume Discussion on Projects Mentioned in projects Two coding questions -----+all+permutation+of+a+string+geeksforgeeks -----/ 2 Puzzle
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Q2. -----+all+permutation+of+a+string+geeksforgeeks -----/
Ans. 
Generate all permutations of a given string using recursion and backtracking.
• Use recursion to generate all possible permutations of the string.

• Use backtracking to backtrack and explore all possible combinations.

• Store each permutation in an array of strings.
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Q1. Technical Interview 45 min Introduce yourself Projects included in Resume Discussion on Projects Mentioned in projects Two coding questions -----+a+string+geeksforgeeks -----/ 3 Puzzle
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Q1. Technical + HR 1 hrs Introduce yourself Projects included in Resume Discussion on Projects Mentioned in projects 3 coding questions ----- ----- ----- 2 Puzzle
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Round duration - 60 minutes
Round difficulty - Easy

Timing: Morning
Environment: Online
Description: This round was conducted immediately after Aptitude Round if you cleared it. 4 Questions in 60 minutes.

Q1. 
MergeSort Linked List Problem Statement
You are given a Singly Linked List of integers. Your task is to sort the list using the 'Merge Sort' algorithm.
Input:
The input consists of a single line contain...read more
Ans. 
Sort a Singly Linked List using Merge Sort algorithm.
• Implement the Merge Sort algorithm for linked lists.

• Divide the list into two halves, sort each half recursively, and then merge them.

• Make sure to handle the base case of an empty or single-node list.

• Example: Input: 4 3 2 1 -1, Output: 1 2 3 4
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Q2. 
Rotate Array Problem Statement
The task is to rotate a given array with N elements to the left by K steps, where K is a non-negative integer.
Input:
The first line contains an integer N representing the...read more
Ans. 
Rotate a given array to the left by K steps.
• Create a new array to store the rotated elements.

• Use modular arithmetic to handle cases where K is greater than the array size.

• Shift elements to the left by K steps and update the new array.

• Return the rotated array as output.
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Q3. 
Problem: Permutations of a String
Given a string STR consisting of lowercase English letters, your task is to return all permutations of the given string in lexicographically increasing order.
Explanatio...read more
Ans. 
Return all permutations of a given string in lexicographically increasing order.
• Use backtracking to generate all permutations of the string.

• Sort the permutations in lexicographical order before printing.

• Ensure the string contains unique characters for correct output.

• Handle multiple test cases by iterating over each case.
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Q4. 
Factorial Calculation Problem
Given an integer N, determine the factorial value of N. The factorial of a number N is the product of all positive integers from 1 to N.
Input:
First line of input: An inte...read more
Ans. 
Calculate factorial of a given number N.
• Iterate from 1 to N and multiply each number to get the factorial value.

• Handle edge cases like N=0 or N=1 separately.

• Use recursion or iteration to calculate factorial efficiently.
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Round duration - 40 minutes
Round difficulty - Medium

Timing: Morning
Environment: Online

Q1. 
Print Series Problem Statement
Given two positive integers N and K, your task is to generate a series of numbers by subtracting K from N until the result is 0 or negative, then adding K back until it reac...read more
Ans. 
Generate a series of numbers by subtracting K from N until 0 or negative, then adding K back to reach N without using loops.
• Create a recursive function to generate the series.

• Subtract K from N until N is 0 or negative, then add K back until N is reached.

• Return the series as an array of integers.
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Q2. 
Unique Element In Sorted Array
Nobita wants to impress Shizuka by correctly guessing her lucky number. Shizuka provides a sorted list where every number appears twice, except for her lucky number, which a...read more
Ans. 
Find the unique element in a sorted array where all other elements appear twice.
• Iterate through the array and XOR all elements to find the unique element.

• Use a hash set to keep track of elements and find the unique one.

• Sort the array and check adjacent elements to find the unique one.
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Q3. 
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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Q4. Write a query to find the Nth highest salary along with the employee name.
Ans. 
Query to find the Nth highest salary with employee name
• Use a subquery to rank the salaries in descending order

• Select the distinct salary from the subquery with LIMIT N-1, 1 to get the Nth highest salary

• Join the main table with the subquery on the salary column to get the employee name
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Round duration - 25 minutes
Round difficulty - Easy

Timing: It was in the morning then rescheduled to evening
Environment: Online

Q1. 
Remove String from Linked List Problem
You are provided with a singly linked list where each node contains a single character, along with a string 'STR'. Your task is to remove all occurrences of the stri...read more
Ans. 
Remove all occurrences of a specified string from a singly linked list by checking from the end of the list.
• Traverse the linked list from the end to efficiently remove the specified string occurrences.

• Update the pointers accordingly after removing the string to maintain the integrity of the linked list.

• Consider edge cases such as when the entire linked list contains the specified string.

• Use a temporary buffer to keep t
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One question relates to Linked list and another related to string

Q1. Circular linked list algorithm
Ans. 
Circular linked list is a data structure where the last node points back to the first node.
• In a circular linked list, each node has a pointer to the next node and the last node points back to the first node.

• Traversal in a circular linked list can start from any node and continue until the starting node is reached again.

• Insertion and deletion operations in a circular linked list are similar to those in a regular linked ...read more
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Q2. String manipulation and logical questioning
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Q3. String creation and deletion
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Q4. DSA problem solving questions
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Q5. Logical questions asked and informed
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2 dsa +1sql leetcode medium tyoe questions

Q1. Resume related questions , my was MERN STACK
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Q2. One dsa question
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Medium level array question was asked on hackerrank.

Q1. Simple string question was asked which required a little thinking and simple implementation.
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Q1. This was a coding round. I was given a screenshot which has dropdowns in it and I had to make the UI of it using react.js
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3 coding question.
40 aptitude related to different topics

Q1. Related to resume
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