Dunnhumby Power BI Developer Interview Questions and Answers

Q1. Normal questions on power bi, sql
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Q2. Normal questions on power bi, sql and service
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Q1. Project related questions
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Q2. DAX and SQL Query
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Q1. Write a DAX query to calculate the YTD running total ensuring that selection of the year should be through slicers & only one year at a time can be selected if more are selected the warning message should ...read more
Ans. 
DAX query for YTD running total with single year selection and warning for multiple selections.
• Use the DATESYTD function to calculate the year-to-date total.

• Implement a measure to check the number of selected years using COUNTROWS and VALUES.

• Display a warning message using a conditional statement if more than one year is selected.

• Example DAX measure: YTD Total = CALCULATE(SUM(Sales[Amount]), DATESYTD(Sales[Date]))

• Examp...read more
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Q2. Write a SQL query to identify the payment id/ transaction ids made at the same merchant with same amount and with same order id using the same credit card however the timestamp in which the transaction hap...read more
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Q1. Explain the types of joins.
Ans. 
Joins are used to combine data from two or more tables based on a related column.
• Inner Join: Returns only the matching rows from both tables.

• Left Join: Returns all the rows from the left table and matching rows from the right table.

• Right Join: Returns all the rows from the right table and matching rows from the left table.

• Full Outer Join: Returns all the rows from both tables, with NULL values in the columns where ther...read more
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Q2. Explain the type of relationships and their use case.
Ans. 
Power BI supports three types of relationships: one-to-one, one-to-many, and many-to-many.
• One-to-one: used when two tables have a unique relationship, such as a person and their social security number.

• One-to-many: used when one record in the first table can have multiple matching records in the second table, such as a customer and their orders.

• Many-to-many: used when multiple records in the first table can have multipl...read more
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Round duration - 60 minutes
Round difficulty - Easy

10 Aptitude questions with difficulty level hard were asked in this test.

Q1. What is the minimum number of planes required to go around the world?
Ans. 
The minimum number of planes required to go around the world is one.
• One plane can fly around the world without needing to stop.

• The plane can refuel mid-air or carry enough fuel for the entire journey.

• Examples: Non-stop flights like the Boeing 787 Dreamliner or Airbus A350 can circumnavigate the globe with one plane.
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Round duration - 60 minutes
Round difficulty - Easy

Technical Interview round with questions based on data structures and algorithms. Questions about previous projects done and my roles on it and my leadership capabilities. Few technical questions from Threads and multi-processing.

Q1. 
Search in a Row-wise and Column-wise Sorted Matrix Problem Statement
You are given an N * N matrix of integers where each row and each column is sorted in increasing order. Your task is to find the positi...read more
Ans. 
Given a sorted N * N matrix, find the position of a target integer 'X'.
• Start from the top-right corner of the matrix and compare the target with the element at that position.

• Based on the comparison, move left or down in the matrix to narrow down the search.

• Repeat the process until the target is found or the search goes out of bounds.

• Return the position of the target if found, else return {-1, -1}.
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Q2. 
Rectangular Numbers Problem Statement
Ninja has a number 'N'. Your task is to generate a pattern where the outer rectangle is filled with the number 'N', and as you move inward, the numbers decrease conse...read more
Ans. 
Generate a pattern with outer rectangle filled with number 'N' and decreasing consecutively inward.
• Start by filling the outermost rectangle with the number 'N'.

• Decrease the numbers consecutively as you move inward towards the center.

• Continue this pattern until you reach the center of the rectangle.
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Round duration - 60 minutes
Round difficulty - Medium

DSA based questions were asked in this round. Questions on implementation of Linux directory structure were also asked.

Q1. 
Binary Array Sorting Problem Statement
You are provided with a binary array, i.e., an array containing only 0s and 1s. Your task is to sort this binary array and return it after sorting.
Input:
 The fir...read more
Ans. 
Yes, the binary array sorting problem can be solved in linear time and constant space using a single traversal.
• Use two pointers approach to swap 0s to the left and 1s to the right.

• Maintain two pointers, one for 0s and one for 1s, and swap elements accordingly.

• Example: Input: [1, 0, 1, 0, 1], Output: [0, 0, 1, 1, 1]
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Q2. 
Next Greater Element Problem Statement
You are given an array arr of length N. For each element in the array, find the next greater element (NGE) that appears to the right. If there is no such greater ele...read more
Ans. 
The task is to find the next greater element for each element in an array to its right, if no greater element exists, return -1.
• Iterate through the array from right to left and use a stack to keep track of elements.

• Pop elements from the stack until a greater element is found or the stack is empty.

• Store the next greater element for each element in the output array.
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Q3. What is the difference between Binary Search Trees (BST) and Tries?
Ans. 
BST is a binary tree structure where each node has at most two children, while Tries are tree structures used for storing strings.
• BST is used for searching, inserting, and deleting elements in a sorted manner.

• Tries are used for storing and searching strings efficiently.

• BST has a hierarchical structure with left and right child nodes.

• Tries have nodes representing characters, forming a tree-like structure for strings.

• Exa...read more
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Round duration - 60 minutes
Round difficulty - Easy

This was a technical round. Questions about previous projects and current one were asked. I was also asked about aptitude problems from the first round and how I understood and approached towards solution?

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 valid configurations recursively and backtrack when a solution is not possible.
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Q2. 
Form a Triangle Problem Statement
You are provided with an integer array/list ARR of length N. Your task is to determine if it is possible to construct at least one non-degenerate triangle using the value...read more
Ans. 
Check if it is possible to form a non-degenerate triangle using the sides provided in the array.
• Check if the sum of any two sides is greater than the third side for all combinations.

• If any such combination exists, return true; otherwise, return false.

• Handle multiple test cases as per the constraints provided.
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Round duration - 30 minutes
Round difficulty - Easy

Behavioral questions and team skills were discussed in this round.