Citadel Interview Questions and Answers

Round duration - 60 minutes
Round difficulty - Easy

The interviewer called my via phone and simultaneously provided me a link where I had to write the code for a given problem. It was scheduled at 12:30 pm, so timing was not an issue. It was a standard DP question involving a 2D matrix. The question was easy and I was able to code it within given time.

Round duration - 60 minutes
Round difficulty - Easy

The interviewer asked me two coding questions in this round.

Q1. Write an efficient program to find the sum of the contiguous subarray within a one-dimensional array of numbers that has the largest sum.
Ans. 
Efficient program to find sum of largest contiguous subarray within a one-dimensional array.
• Use Kadane's algorithm to find the maximum sum subarray in O(n) time complexity.

• Initialize max_sum and current_sum to 0, iterate through array updating current_sum and max_sum.

• Return max_sum as the result.
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Round duration - 60 minutes
Round difficulty - Easy

This was on-site round at their Bangalore office. The interviewer was friendly and helpful. The interview held inside a conference room.

Q1. 
DFS Traversal Problem Statement
Given an undirected and disconnected graph G(V, E), where V is the number of vertices and E is the number of edges, the connections between vertices are provided in the 'GR...read more
Ans. 
DFS traversal problem to find connected components in an undirected and disconnected graph.
• Use Depth First Search (DFS) algorithm to traverse the graph and find connected components

• Maintain a visited array to keep track of visited vertices

• Iterate through all vertices and perform DFS on unvisited vertices to find connected components
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Round duration - 60 minutes
Round difficulty - Easy

This was the next round of the onsite interviews. Took place in the same conference room as that of the previous round.

Round duration - 60 minutes
Round difficulty - Easy

This was the third round of the onsite interview. 
 

Round duration - 90 minutes
Round difficulty - Medium

3 coding Questions:
1st : Easy question based on simple loop iteration
2nd :Medium level Dp question 
3rd : Medium level tree question(where we were not just required to complete the tree function but to build whole bst from 
scratch) 

It was conducted from 1:30 - 3:00 pm.
The coding platform was very good (as auto indentation and auto completion of brackets were there)
having camera on.

Q1. 
Selling Stock Problem Statement
You are given the stock prices for N days. Each day i signifies the price of a stock on that day. Your goal is to calculate the maximum profit that can be achieved by buyin...read more
Ans. 
Calculate maximum profit by buying and selling stocks on different days.
• Iterate through the stock prices and buy on the day when the price is lower than the next day's price, and sell on the day when the price is higher than the next day's price.

• Keep track of the total profit earned by summing up the differences between buying and selling prices.

• Return the total profit as the maximum profit that can be earned.
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Q2. 
Minimum Time to Burn a Binary Tree from a Leaf Node
You are given a binary tree with 'N' unique nodes, and a specific start node from where the fire will begin. The task is to determine the time in minute...read more
Ans. 
The task is to determine the time in minutes required to burn the entire binary tree starting from a given node.
• Traverse the tree from the given start node to calculate the time taken to burn the entire tree.

• Use a queue to keep track of nodes and their burning time.

• Increment the burning time for each level of nodes until the entire tree is burned.
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Round duration - 75-80 minutes
Round difficulty - Hard

This was a completely technical coding round where I was asked to solve the problems of data structures.
The codepad where i was asked to code was fine,
The interviewer was very friendly and was helpful and understanding.
I also asked him about his work and experience in the company and some other questions.

Q1. 
Matrix Maximum Path Sum Problem
Given an N*M matrix filled with integer numbers, your task is to find the maximum path sum starting from any cell in the first row and ending at any cell in the last row. Y...read more
Ans. 
Find the maximum path sum in a matrix from the first to the last row with specific movement rules.
• Use dynamic programming to store maximum sums at each cell.

• Start from the first row and iterate downwards.

• For each cell, consider the maximum sum from the cell above, the cell diagonally left above, and the cell diagonally right above.

• Update the current cell's value with the maximum path sum leading to it.

• The result will b...read more
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Round duration - 45 minutes
Round difficulty - Easy

It was held on Gmeet platform
The interviewer was very experienced person and was very nice too.
He made me comfortable by first introducing himself in a very detailed way and then asking me mine introduction
Since I feel that his internet connection was not very good so he turned off his camera but I decided not to turn off mine as in online interviews your face reviles your confidence 
the interviewer mostly asked me questions about my interests in technical field and the project that I have done

Round duration - 90 minutes
Round difficulty - Medium

The coding round consisted of 3 coding questions. 1st question was of 20 marks, 2nd and 3rd of 50 marks.

Q1. 
Minimum Number of Operations Problem Statement
Given an array 'ARR' consisting of 'N' positive integers, determine the minimum number of operations needed to make all elements of the array equal. You may ...read more
Ans. 
Determine minimum operations to make all array elements equal using addition, subtraction, multiplication, or division.
• Iterate through array to find the minimum and maximum values

• Calculate the difference between the maximum and minimum values

• Return the difference as the minimum number of operations needed
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Q2. 
Avoiding Traps Problem Statement
Given an array of obstacles' coordinates, determine the minimal jump length to reach beyond all obstacles starting from coordinate 0 while avoiding landing on any obstacle...read more
Ans. 
Find the minimal jump length to bypass all obstacles while avoiding landing on any obstacle.
• Iterate through the obstacle coordinates to find the maximum coordinate.

• Calculate the minimum jump length needed to bypass all obstacles.

• Ensure the jump length consistently avoids all obstacle points.

• The final jump can overshoot the line's end point.
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Q3. 
Longest Consecutive Sequence Problem Statement
You are given an unsorted array/list ‘ARR’ of ‘N’ integers. Your task is to return the length of the longest consecutive sequence.
The consecutive sequence ...read more
Ans. 
Find the length of the longest consecutive sequence in an unsorted array of integers.
• Sort the array to make it easier to identify consecutive sequences.

• Use a set to store unique elements and check for consecutive numbers.

• Track the length of consecutive sequences and update the maximum length found.

• Handle duplicates by counting only one occurrence in the consecutive sequence.
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Round duration - 45 minutes
Round difficulty - Easy

Timing: 10:15 - 11:00 am.
The interview was online from home.

Round duration - 45 minutes
Round difficulty - Medium

Timing: 2:15 - 3:00 PM
The interview was online from home.
There were a few audio cuts in the video call but we were able to manage regardless.

Q1. 
Reverse a String Problem Statement
Given a string STR containing characters from [a-z], [A-Z], [0-9], and special characters, determine the reverse of the string.
Input:
The input starts with a single i...read more
Ans. 
Reverse a given string containing characters from [a-z], [A-Z], [0-9], and special characters.
• Iterate through the characters of the string in reverse order and append them to a new string.

• Use built-in functions like reverse() or StringBuilder in languages like Python or Java for efficient reversal.

• Handle special characters and numbers along with alphabets while reversing the string.

• Ensure to print each reversed string ...read more
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Q1. Basics of Java and selenium
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Q1. What are your strengths and weaknesses?
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