McKinsey & Company Database Developer Interview Questions and Answers

Round duration - 90 minutes
Round difficulty - Medium

This test consists of two coding questions and some MCQ regarding computer fundamentals.

Q1. 
Kevin and His Cards Problem Statement
Kevin has two packs of cards. The first pack contains N cards, and the second contains M cards. Each card has an integer written on it. Determine two results: the tot...read more
Ans. 
Find total distinct card types and common card types between two packs of cards.
• Create a set to store distinct card types when combining both packs.

• Iterate through each pack and add card types to the set.

• Find the intersection of card types between the two packs to get common card types.
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Q2. 
Allocate Books Problem Statement
Given an array of integers arr, where arr[i] represents the number of pages in the i-th book, and an integer m representing the number of students, allocate all the books ...read more
Ans. 
Allocate books to students in a way that minimizes the maximum number of pages assigned to a student.
• Iterate through all possible allocations of books to students.

• Calculate the maximum number of pages assigned to a student for each allocation.

• Return the minimum of these maximums as the result.
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Round duration - 40 minutes
Round difficulty - Easy

It was a technical round that is based on DSA and computer fundamentals.

Q1. 
Reverse Linked List Problem Statement
Given a singly linked list of integers, return the head of the reversed linked list.
Example:
Initial linked list: 1 -> 2 -> 3 -> 4 -> NULL
Reversed link...read more
Ans. 
Reverse a singly linked list of integers and return the head of the reversed linked list.
• Iterate through the linked list and reverse the pointers to point to the previous node instead of the next node.

• Use three pointers - prev, current, and next to reverse the linked list in O(N) time and O(1) space complexity.

• Update the head of the reversed linked list as the last node encountered during the reversal process.
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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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1. One question was given to be solved in 1 hour. Question was medium level based on strings.

Q1. 1. 1:1 interview, mostly discussion around OOPS concepts and some basic dynamic programming questions.
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1. 3 questions were given out of which any 2 needed to be solved. 1 question related to Database design and query, 2 questions related to DSA, both DSA questions were medium-hard type based on Dynamic programming and graph.
I solved one Dynamic programming question and Database question.

Q1. 1. This round was the follow up of last case study round. Interviewer gave various use cases to test on the algorithms that I had written. Some discussion related to OOPS concepts and Database design quest...read more
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Q1. It was final discussion, mostly around cultural fit and classic HR questions. It was easy one, I'd say.
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