HashedIn by Deloitte Interview Questions, Process, and Tips

Round duration - 90 minutes
Round difficulty - Medium

3 coding questions were there

Q1. 
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 iterating through 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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Q2. 
Longest Increasing Subsequence Problem Statement
Given an array of integers with 'N' elements, determine the length of the longest subsequence where each element is greater than the previous element. This...read more
Ans. 
Find the length of the longest strictly increasing subsequence in an array of integers.
• Use dynamic programming to solve this problem efficiently.

• Initialize an array to store the length of the longest increasing subsequence ending at each index.

• Iterate through the array and update the length of the longest increasing subsequence for each element.

• Return the maximum value in the array as the result.
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Round duration - 60 Minutes
Round difficulty - Medium

2 coding were asked

Q1. 
Minimum Number of Platforms Needed Problem Statement
You are given the arrival and departure times of N trains at a railway station for a particular day. Your task is to determine the minimum number of pl...read more
Ans. 
Determine the minimum number of platforms needed at a railway station based on arrival and departure times of trains.
• Sort the arrival and departure times in ascending order.

• Use two pointers to keep track of overlapping schedules.

• Increment the platform count when a new train arrives before the previous one departs.

• Return the maximum platform count needed.
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Round duration - 60 Minutes
Round difficulty - Medium

2 coding questions

Q1. 
Lowest Common Ancestor (LCA) Problem Statement
Understanding the concept of Lowest Common Ancestor (LCA) in graph theory and computer science is essential.
Consider a rooted tree ‘T’ containing ‘N’ nodes...read more
Ans. 
The Lowest Common Ancestor (LCA) problem involves finding the lowest node in a tree that is an ancestor of two given nodes.
• LCA is the lowest node in a tree that is an ancestor of both given nodes.

• The tree is rooted at node 1 for each test case.

• Paths from each node to the root are considered to find the LCA.

• Constraints include the number of test cases, nodes, queries, and node values.

• Time limit for the solution is 1 sec
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Round duration - 15 Minutes
Round difficulty - Easy

Basic questions like "tell me about family members and their occupation", "why hashedin" are asked.

Round duration - 40 minutes
Round difficulty - Easy

17 candidates were shortlisted for the interview.
There were 2 coding questions asked of easy level. I had to explain my approach and write the code in google doc.

Q1. 
Check if Two Trees are Mirror
Given two arbitrary binary trees, your task is to determine whether these two trees are mirrors of each other.
Explanation:
Two trees are considered mirror of each other if...read more
Ans. 
Check if two binary trees are mirrors of each other based on specific criteria.
• Compare the roots of both trees.

• Check if the left subtree of the first tree is the mirror of the right subtree of the second tree.

• Verify if the right subtree of the first tree is the mirror of the left subtree of the second tree.
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Q2. 
Count Ways to Reach the N-th Stair Problem Statement
You are provided with a number of stairs, and initially, you are located at the 0th stair. You need to reach the Nth stair, and you can climb one or tw...read more
Ans. 
The problem involves finding the number of distinct ways to climb N stairs by taking 1 or 2 steps at a time.
• Use dynamic programming to solve the problem efficiently.

• The number of ways to reach the Nth stair is the sum of the number of ways to reach the (N-1)th stair and the (N-2)th stair.

• Handle base cases for N=0 and N=1 separately.

• Consider using modulo operation to avoid overflow for large values of N.
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Round duration - 90 Minutes
Round difficulty - Easy

The round was held in evening. There were 4 questions asked and the interviewer was more interested in the running code with several test cases rather than my explaination.

Q1. 
Excel Column Number Conversion
Given a column title as it appears in an Excel sheet, your task is to return its corresponding column number.
Example:
Input:
S = "AB"
Output:
28
Explanation:
The seq...read more
Ans. 
Convert Excel column title to corresponding column number.
• Iterate through each character in the input string

• Calculate the corresponding value of each character based on its position in the alphabet

• Multiply the value by 26 raised to the power of its position from the right in the input string

• Sum up all the values to get the final column number
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Q2. 
Increase Number By 1 Problem Statement
Given an array of integers NUM that consists of N elements, where the array represents the digits of a number, your task is to add 1 to this number. The number is po...read more
Ans. 
Given an array representing digits of a number, add 1 to the number.
• Iterate through the array from right to left, starting with the least significant digit.

• Add 1 to the current digit and check if it becomes 10. If so, set it to 0 and carry over to the next digit.

• Handle the case where the most significant digit needs to be incremented by creating a new array with an extra digit.
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Q3. 
Ways To Make Coin Change
Given an infinite supply of coins of varying denominations, determine the total number of ways to make change for a specified value using these coins. If it's not possible to make...read more
Ans. 
The task is to determine the total number of ways to make change for a specified value using given denominations.
• Create a dynamic programming table to store the number of ways to make change for each value up to the target value.

• Iterate through each denomination and update the table accordingly based on the current denomination.

• The final value in the table will represent the total number of ways to make change for the ...read more
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Q4. 
Tic-Tac-Toe Design Problem
Design a 2-player Tic-Tac-Toe game played on an N * N grid where Player 1 uses ‘X’ and Player 2 uses ‘O’. A move is always valid and occupies an empty spot.
If a player places ...read more
Ans. 
Design a 2-player Tic-Tac-Toe game on an N x N grid where players place their marks to win by getting N marks in a row.
• Create a 2D array to represent the game board.

• Implement a function to check for a win after each move.

• Handle player moves and update the board accordingly.

• Return the result of each move (0, 1, or 2) based on the game state.

• Consider horizontal, vertical, and diagonal win conditions.
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3 coding questions needed to be completed in 1.5 hours.

Q1. Q1 - Sort the string according to frequency of characters
Ans. 
Sort a string based on the frequency of its characters.
• Create a hash table to store the frequency of each character.

• Sort the characters based on their frequency using a sorting algorithm.

• Reconstruct the string based on the sorted characters and their frequency.
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Q1. Q1 - Pre order traversal without recursion. Q2 - Reverse a linked list.
Ans. 
Q1 - Pre order traversal without recursion. Q2 - Reverse a linked list.
• Q1: Use a stack to keep track of nodes. Start with root, push it to stack. Pop top node, print it, push right and left children to stack.

• Q2: Traverse the linked list and change the direction of the pointers. Set the head of the reversed list as the last node of the original list.
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Round duration - 60 minutes
Round difficulty - Medium

Q1. 
Four Sum Problem Statement
You are provided with an array/list 'ARR' consisting of 'N' integers and an integer 'TARGET'. The task is to determine if there exist four distinct numbers in 'ARR' such that th...read more
Ans. 
The task is to determine if there exist four distinct numbers in an array that sum up to a given target value.
• Iterate through all possible combinations of four distinct numbers in the array.

• Use a nested loop to check all combinations efficiently.

• Keep track of the sum of each combination and compare it with the target value.

• Return 'Yes' if a valid combination is found, otherwise return 'No'.
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Round duration - 50 minutes
Round difficulty - Medium

Q1. 
Detect and Remove Loop in Linked List
For a given singly linked list, identify if a loop exists and remove it, adjusting the linked list in place. Return the modified linked list.
Expected Complexity:
A...read more
Ans. 
Detect and remove loop in a singly linked list in place with O(n) time complexity and O(1) space complexity.
• Use Floyd's Tortoise and Hare algorithm to detect the loop in the linked list.

• Once the loop is detected, find the start of the loop using the same algorithm.

• Adjust the pointers to remove the loop and return the modified linked list.

• Example: For input 5 2 and elements 1 2 3 4 5, output should be 1 2 3 4 5.
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Q2. 
Lowest Common Ancestor in a BST Problem Statement
You're provided with a Binary Search Tree (BST) containing 'N' nodes with integer values and two specific nodes, 'P' and 'Q'.
Your task is to identify th...read more
Ans. 
Find the lowest common ancestor of two nodes in a Binary Search Tree.
• Traverse the BST from the root to find the LCA of the given nodes.

• Compare the values of the nodes with the values of P and Q to determine the LCA.

• Handle cases where one node is the ancestor of the other or when one of the nodes is the root.

• Use recursion to efficiently find the LCA in the BST.

• Consider edge cases such as when the nodes are not present i
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Round duration - 120 Minutes
Round difficulty - Medium

Q1. 
Triplets with Given Sum Problem
Given an array or list ARR consisting of N integers, your task is to identify all distinct triplets within the array that sum up to a specified number K.
Explanation:
A t...read more
Ans. 
The task is to find all distinct triplets in an array that sum up to a specified number.
• Iterate through all possible triplets using three nested loops.

• Check if the sum of the triplet equals the target sum.

• Print the triplet if found, else print -1.
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Q2. Can you describe a situation where you were given a schema and asked to write SQL queries based on it?
Ans. 
Yes, I was given a schema and asked to write SQL queries based on it.
• I was given a schema for a database that included tables, columns, and relationships between them.

• I had to write SQL queries to retrieve specific data from the database based on the schema provided.

• For example, I was asked to write a query to retrieve all customers who made a purchase in the last month.

• I had to understand the schema to correctly write...read more
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Round duration - 20 Minutes
Round difficulty - Easy

Q1. Can you tell me about yourself and what new things you did during the lockdown?
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