30+ DS Group Interview Questions and Answers

Find the distance between the closest pair of points in a plane given an array of points.

• Calculate the distance between each pair of points using the formula provided.

• Keep track of the minimum distance found so far.

• Optimize the solution to avoid unnecessary calculations by considering only relevant pairs.

• Consider using a data structure like a priority queue or sorting to improve efficiency.

• Handle edge cases like when there are only two points in the array.

Calculate the total number of unique rectangles that can be formed within a grid using its rows and columns.

• Iterate through all possible combinations of rows and columns to calculate the number of unique rectangles

• Use the formula (M * (M + 1) / 2) * (N * (N + 1) / 2) to find the total number of rectangles

• Return the total number of unique rectangles for each test case

Reconstruct original sequence of cards given a specific sequence of cards placed on table.

• The last card placed on the table must be 10.

• The second last card placed on the table must be 5 or 6.

• The first card placed on the table must be either 1 or 2.

• Use trial and error method to reconstruct the original sequence.

Find the Lowest Common Ancestor (LCA) of two nodes in a binary tree.

• Traverse the binary tree to find the paths from the root to nodes X and Y.

• Compare the paths to find the last common node, which is the LCA.

• Handle cases where one node is an ancestor of the other.

• Consider edge cases like when X or Y is the root node.

• Implement a recursive or iterative solution to find the LCA efficiently.

Identify all starting indices of anagrams of a given string in another string.

• Iterate through the main string using a sliding window approach.

• Use a hashmap to keep track of characters in the anagram string.

• Compare the hashmap of the anagram string with the current window of characters in the main string.

• If the hashmaps match, add the starting index of the window to the result array.

Given a Binary Search Tree and a target value, determine if there exist two unique elements in the BST such that their sum equals the target.

• Traverse the BST in-order to get a sorted array of elements.

• Use two pointers approach to find the pair with the given sum.

• Consider edge cases like null nodes and duplicate elements.

Zig Zag Tree Traversal involves alternating directions while traversing a binary tree level by level.

• Implement a level order traversal of the binary tree.

• Alternate the direction of traversal for each level.

• Use a queue data structure to keep track of nodes at each level.

• Handle null nodes appropriately to maintain the zigzag pattern.

• Example: For input 1 2 3 4 -1 5 6 -1 7 -1 -1 -1 -1 -1 -1, the output should be 1 3 2 4 5 6 7.

The task is to determine whether tree S is a subtree of tree T, matching structure and node values.

• Parse the input level order traversal of both trees T and S

• Check if tree S is a subtree of tree T by comparing their structures and node values

• Output 'true' if S is a subtree of T, otherwise 'false'

Find the largest rectangular area in a histogram given the heights of the bars.

• Use a stack to keep track of the indices of the bars in non-decreasing order of heights.

• Calculate the area of the rectangle with each bar as the smallest bar and update the maximum area.

• Handle the case when the stack is not empty after processing all bars to calculate the remaining areas.

• Example: For HEIGHTS = [2, 1, 5, 6, 2, 3], the largest rectangle has an area of 10.

Reverse a given singly linked list by changing the links between nodes.

• Iterate through the linked list and reverse the links between nodes.

• Keep track of the previous, current, and next nodes while reversing the links.

• Update the head of the linked list to point to the last node after reversal.

Detect if a singly linked list forms a cycle by checking if a node's next reference points back to a previous node.

• Use two pointers, one moving at double the speed of the other, to detect a cycle.

• 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.

Perform in-order traversal of a binary tree without recursion.

• Use a stack to simulate the recursive process of in-order traversal

• Start with the root node and keep traversing left until reaching a null node, then pop from stack and move to right node

• Keep track of visited nodes to avoid revisiting them

• Return the in-order traversal list

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 current element.

• 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}.

Java function to return subnet mask of IP and URL after www.

• Read the file and store IP addresses and URLs in separate arrays

• Use regex to extract subnet mask from IP address

• Use substring to extract URL after www.

• Return subnet mask and URL as separate strings

Calculate the Nth term of the Fibonacci series using a recursive formula.

• Use the formula F(n) = F(n-1) + F(n-2) to calculate the Nth Fibonacci number.

• Start with base cases F(1) = 1 and F(2) = 1.

• Continue recursively calculating Fibonacci numbers until reaching the desired N.

• Ensure to handle edge cases and constraints such as 1 ≤ N ≤ 10000.

For Snapdeal's shoe section, I would design a DBMS with separate entities for Sports and Casual Shoes.

• Create a main entity for shoes with attributes like brand, size, color, etc.

• Create separate entities for Sports and Casual Shoes with attributes specific to each category.

• Link the Sports and Casual Shoe entities to the main Shoe entity using a foreign key.

• Use indexing and normalization techniques to optimize performance and reduce redundancy.

• Consider implementing a search fea...read more

Pick a fruit from the jar labeled 'Apples and Oranges' to correctly label all jars.

• Pick a fruit from the jar labeled 'Apples and Oranges'.

• If you pick an apple, label the jar as 'Apples'.

• If you pick an orange, label the jar as 'Oranges'.

• Label the remaining jars accordingly based on the above information.

Burn one rope from both ends and the other rope from one end.

• Light one rope from both ends and the other rope from one end.

• When the first rope burns completely, 30 minutes have passed.

• Then, immediately light the other end of the second rope.

• When the second rope burns completely, 15 more minutes have passed.

• Total time elapsed is 45 minutes.

Merge two sorted arrays into one sorted array of larger size

• Create a new array of size m+n

• Compare the last elements of both arrays and insert the larger one at the end of the new array

• Repeat until all elements are merged

• If any elements are left in the smaller array, insert them at the beginning of the new array

• Time complexity: O(m+n)

• Example: arr1=[1,3,5,7,0,0,0], arr2=[2,4,6], output=[1,2,3,4,5,6,7]

The question asks to find the count of words in a dictionary that can be formed by a given number.

• Iterate through each word in the dictionary

• Check if the characters in the word can be formed using the given number

• Increment the count if the word can be formed

DNS servers translate domain names into IP addresses to enable communication between devices on the internet.

• DNS servers act as a phone book for the internet, translating domain names into IP addresses.

• When a user types a domain name into their browser, the browser sends a request to a DNS server to resolve the domain name into an IP address.

• DNS servers operate in a hierarchical system, with root servers at the top, followed by top-level domain servers, and then authoritative...read more

Finding lowest common ancestor of two nodes in binary tree

• Traverse the tree from root to both nodes and store the paths in separate arrays

• Compare the paths to find the last common node

• Return the last common node as the lowest common ancestor

• Use recursion to traverse the tree efficiently

Algorithm to find LCM of all numbers from 1 to n and its time complexity

• Find prime factors of all numbers from 1 to n

• For each prime factor, find the highest power it appears in any number from 1 to n

• Multiply all prime factors raised to their highest power to get LCM

• Time complexity: O(n*log(log(n)))

The number is 7744.

• The number must end in 00 or 44.

• The square root of the number must be a whole number.

• The only possible number is 7744.

To find the length of non-looped linked list, we need to traverse the list and count the number of nodes.

• Traverse the linked list using a pointer and count the number of nodes until the end of the list is reached.

• If a loop is encountered, break out of the loop and continue counting until the end of the list.

• Return the count as the length of the non-looped linked list.

A program to check if a number is a palindrome or not.

• Convert the number to a string

• Reverse the string

• Compare the original and reversed string

• If they are the same, the number is a palindrome

Use two identical wires to measure 45 minutes by burning them at different ends.

• Burn one end of the first wire and both ends of the second wire simultaneously.

• When the first wire burns completely (30 minutes), light the other end of the second wire.

• When the second wire burns completely (15 minutes), 45 minutes have passed.

Inner join returns only the matching rows between two tables, while outer join returns all rows from one table and matching rows from the other.

• Inner join combines rows from two tables based on a matching column.

• Outer join returns all rows from one table and matching rows from the other.

• Left outer join returns all rows from the left table and matching rows from the right table.

• Right outer join returns all rows from the right table and matching rows from the left table.

• Full ou...read more

To find the merging point of two linked lists

• Traverse both linked lists and find their lengths

• Move the pointer of the longer list by the difference in lengths

• Traverse both lists simultaneously until they meet at the merging point

NoSQL databases are flexible, scalable, and can handle large amounts of unstructured data.

• NoSQL databases are schema-less, allowing for easy and flexible data modeling.

• They can handle large amounts of unstructured data, making them suitable for big data applications.

• NoSQL databases are highly scalable and can easily handle high traffic and large user bases.

• They provide horizontal scalability by distributing data across multiple servers.

• NoSQL databases are often used in real-t...read more

The number of rectangles in an MxN matrix can be calculated using a formula.

• The formula is (M * (M + 1) * N * (N + 1)) / 4

• The matrix can be divided into smaller sub-matrices to count the rectangles

• The number of rectangles can also be calculated by counting all possible pairs of rows and columns

To find square root of a number, use Math.sqrt() function in JavaScript.

• Use Math.sqrt() function in JavaScript to find square root of a number.

• For example, Math.sqrt(16) will return 4.

• If the number is negative, Math.sqrt() will return NaN.

An outer join combines rows from two tables even if there is no match between the columns being joined.

• Returns all rows from both tables, filling in missing values with NULL

• Useful for finding unmatched rows between two tables

• Types of outer joins include LEFT OUTER JOIN, RIGHT OUTER JOIN, and FULL OUTER JOIN

Inner Join is a SQL operation that combines rows from two tables based on a related column between them.

• Inner Join returns only the rows that have matching values in both tables.

• It is used to retrieve data that exists in both tables.

• Example: SELECT * FROM table1 INNER JOIN table2 ON table1.column = table2.column;