Dunnhumby Software Developer Interview Questions and Answers

Round duration - 60 minutes
Round difficulty - Medium

This was a test round where 10 aptitude based questions were to be solved in 60 minutes

Q1. You have 5 pirates and 100 gold coins. The challenge is to determine how the pirates will divide the coins among themselves based on their ranking and the rules they follow.
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Round duration - 60 minutes
Round difficulty - Medium

They took us to the lab for this on and we were each given a paper with a program on it. It was all mixed as in each person got a different paper, You have around an hour to finish coding. after which you have to explain your code. They also gave wrong or incorrect inputs and see how your code handles these exceptions.

Q1. 
Reverse the String Problem Statement
You are given a string STR which contains alphabets, numbers, and special characters. Your task is to reverse the string.
Example:
Input:
STR = "abcde"
Output:
"e...read more
Ans. 
Reverse a given string containing alphabets, numbers, and special characters.
• Iterate through the string from the end to the beginning and append each character 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 consider the constraints provided in th...read more
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Q2. 
K Largest Elements Problem Statement
Given an unsorted array containing 'N' integers, you are required to find 'K' largest elements from the array and return them in non-decreasing order.
Input:
The fir...read more
Ans. 
Implement a function to find K largest elements in an unsorted array in non-decreasing order.
• Create a min heap of size K and insert the first K elements of the array

• For each remaining element, if it is larger than the root of the heap, replace the root with the element and heapify

• Finally, the heap will contain the K largest elements in non-decreasing order
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Q3. 
Remove Character from String Problem Statement
Given a string str and a character 'X', develop a function to eliminate all instances of 'X' from str and return the resulting string.
Input:
The first lin...read more
Ans. 
Develop a function to remove all instances of a given character from a string.
• Iterate through the string and build a new string excluding the specified character.

• Use a StringBuilder or similar data structure for efficient string manipulation.

• Handle edge cases like empty string or character not found in the input string.

• Ensure the function completes within the given time constraint.
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Q4. 
Triangle of Numbers Pattern
Ninja is tasked with printing a triangle pattern based on a given number 'N' for any test case.
Example:
Input:
N = 4
Output:
   1
  232
 34545
4567654
Explanation:
The pat...read more
Ans. 
Print a triangle pattern of numbers based on a given number 'N'.
• Iterate through each row and column to determine the numbers to print

• Use a combination of spaces and numbers to align the pattern correctly

• Increment the numbers in each row based on the row number
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Round duration - 60 minutes
Round difficulty - Easy

Compared to the other round this is more tech oriented. Lot more tech questions. It is of normal difficulty and is not that hard to clear, you only need to know the basics.
Very basic of Data Structure and Oracle knowledge enough. Lots of simple questions from data structures(insert into heaps etc). They did not ask to write code for DS, but rather to explain the logic through diagrams. For some complicated question, they expect how much you brainstorm ideas in solving

Q1. 
Convert Binary Tree to Mirror Tree
Convert a given binary tree into its mirror tree, where the left and right children of all non-leaf nodes are interchanged.
Input:
An integer ‘T’ denoting the number o...read more
Ans. 
Convert a binary tree into its mirror tree by interchanging left and right children of non-leaf nodes.
• Traverse the tree in postorder fashion and swap the left and right children of each node.

• Use recursion to solve the problem efficiently.

• Modify the binary tree in place without creating a new tree.
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Q2. 
Heap Sort Problem Statement
Given an array ARR consisting of N integers, your task is to use the Heap sort algorithm to arrange the array in non-decreasing order.
Input:
The first line of the input cont...read more
Ans. 
Implement the Heap sort algorithm to arrange an array in non-decreasing order.
• Implement the Heap sort algorithm to sort the given array in non-decreasing order

• Use a max heap to sort the array in non-decreasing order

• Time complexity of Heap sort is O(n log n)
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Q3. What is indexing in the context of databases?
Ans. 
Indexing in databases is a technique used to improve the speed of data retrieval by creating a data structure that allows for quick lookups.
• Indexes are created on specific columns in a database table to speed up queries that search for data in those columns.

• Indexes work similar to the index of a book, allowing the database to quickly locate the desired data without having to scan the entire table.

• Examples of indexes in...read more
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Q4. Which data structure is better for your use case: a B Tree or a Hash Table?
Ans. 
Hash Table is better for fast lookups and insertions, while B Tree is better for range queries and ordered traversal.
• Use Hash Table for fast lookups and insertions with O(1) average time complexity.

• Use B Tree for range queries and ordered traversal with O(log n) time complexity.

• Consider the size of the dataset and the specific operations needed to determine the best data structure.
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Round duration - 30 minutes
Round difficulty - Easy

This round lasted for around 30 minutes. It more of a character analysis round with a lot of HR type questions.

Round duration - 60 minutes
Round difficulty - Medium

This test consisted of 10 questions with no negative marking to test my problem solving ability.

Round duration - 60 minutes
Round difficulty - Medium

Technical Interview round with questions based on DSA and algorithms.

Q1. 
Word Distance Calculation
Given a document represented as an array/list ARR of words with length N, find the smallest distance between two given words for multiple queries. The distance is defined as the ...read more
Ans. 
Find the smallest distance between two words in a document for multiple queries.
• Iterate through the document to find the indices of the given words in the document array.

• Calculate the distance between the two indices for each query.

• Return the smallest distance or 'N' if a word from the query is not present in the document.
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Q2. 
Sudoku Solver Problem Statement
Given a 9 x 9 2D matrix 'MATRIX', where some cells are filled with digits (1-9) and others are empty (denoted by 0), determine if there is a way to fill the empty cells suc...read more
Ans. 
The task is to determine if a given 9x9 Sudoku puzzle can be solved.
• Check if each row, column, and 3x3 subgrid contains all numbers from 1 to 9 without repetition.

• Iterate through each empty cell and try filling it with a valid number, then recursively check if the puzzle can be solved.

• If all empty cells are filled without violating Sudoku rules, output 'yes'; otherwise, output 'no'.
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Round duration - 60 minutes
Round difficulty - Easy

You will be having 2 or 3 members per panel and questions may be from databases , object oriented programming, operating systems, Linux commands and algorithm may be asked for problems

Q1. 
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 forms a cycle by checking if a node's next points back to a previous node.
• Traverse the linked list using two pointers, one moving at double the speed of the other

• If the two pointers meet at any point, there is a cycle in the linked list

• If one of the pointers reaches the end of the list (null), there is no cycle
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Q2. 
Level Order Traversal Problem Statement
Given a binary tree of integers, return the level order traversal of the binary tree.
Input:
The first line contains an integer 'T', representing the number of te...read more
Ans. 
The task is to implement a function that returns the level order traversal of a binary tree given in level order.
• Create a queue to store nodes for level order traversal

• Start with the root node and enqueue it

• While the queue is not empty, dequeue a node, print its value, and enqueue its children

• Repeat until all nodes are traversed
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Q3. What are virtual functions?
Ans. 
Virtual functions are functions in a base class that are overridden in derived classes, allowing for polymorphic behavior.
• Virtual functions are declared in a base class with the 'virtual' keyword.

• They are meant to be overridden in derived classes to provide specific implementations.

• They allow for polymorphism, where a pointer to a base class can call a derived class's overridden function.

• Example: virtual void display()
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Q1. Technology questions were asked as per experience
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Q1. Hr related questions were asking more of behaviourial
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Q1. Shallow copy and deep copy
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Q2. What is Pure component
Ans. 
A Pure component is a component in React that does not have any state or lifecycle methods, resulting in improved performance.
• Pure components are used to prevent unnecessary re-renders in React applications.

• Pure components implement shouldComponentUpdate method with shallow comparison of props and state.

• Examples of Pure components include functional components and class components that extend PureComponent class.
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Basic .net concept question and 2 leetcode medium question.
1) find a target element within a rotated search array (complexity < 0(N))

Q1. How would you handle scenerios where if you have 1000 request comming and you can handle 10 request at max
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Q1. Who do you test your django apps?
Ans. 
I test my Django apps using automated testing tools and manual testing methods.
• I use Django's built-in testing framework to write unit tests for individual components of the app.

• I also use tools like pytest and Selenium for automated testing of the app's functionality.

• I perform manual testing to ensure the app works as expected in real-world scenarios.

• I use tools like Django Debug Toolbar to identify and fix any perfor
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Q2. Count the number of vowels in a string.
Ans. 
Count the number of vowels in a given string.
• Iterate through each character in the string and check if it is a vowel (a, e, i, o, u).

• Increment a counter for each vowel found.

• Return the total count of vowels in the string.
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Q1. Given the start and end times of the meetings, how can you determine if you are able to attend all of them?
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