Top 250 Data Structures Interview Questions and Answers

Check if a given singly linked list of integers is a palindrome or not.

• Traverse the linked list to find the middle element using slow and fast pointers.

• Reverse the second half of the linked list.

• Compare the first half with the reversed second half to...read more

The task is to determine if the given binary tree nodes form exactly one valid binary tree.

• Check if there is only one root node (a node with no parent)

• Check if each node has at most one parent

• Check if there are no cycles in the tree

• Check if all nodes...read more

Remove duplicate elements from an Array

• Use the Set object to remove duplicate elements

• Convert the Set back to an array using the spread operator

• If the array contains objects, use a custom comparison function

Stack is LIFO and Queue is FIFO data structure. Stack is like a stack of plates and Queue is like a queue of people.

• Stack is Last In First Out (LIFO) and Queue is First In First Out (FIFO)

• Stack is like a stack of plates where the last plate added is ...read more

A combination of array and hashmap can be used to design the underlying data structures for an educational institution's website.

• Use an array to store the departments available in the institution.

• Each department can be represented as a key in the has...read more

DS algorithm for tree traversal is used to visit each node of a tree exactly once.

• Depth First Search (DFS) - Preorder, Inorder, Postorder

• Breadth First Search (BFS)

• DFS is recursive while BFS uses a queue

• Preorder - Root, Left, Right

• Inorder - Left, Root...read more

Yes, we can implement a stack using two queues.

• Push operation: Enqueue the element to the first queue.

• Pop operation: Dequeue all elements from the first queue and enqueue them to the second queue until the last element. Dequeue and return the last el...read more

To create a custom read-only list, use the ReadOnlyCollection class in C#.

• Create a List<T> object with the desired elements.

• Use the AsReadOnly() method to create a read-only wrapper around the list.

• Use the ReadOnlyCollection<T> class to create a trul...read more

An array of key-value pairs is the best data structure for a dictionary.

• Use a hash table or a balanced tree to implement the dictionary.

• Keys should be unique and immutable.

• Values can be any data type.

• Access time should be O(1) or O(log n) depending o...read more

Given an array of integers, generate a new array with the squares of each element sorted in increasing order.

• Iterate through the array and square each element

• Sort the squared elements in increasing order

• Return the sorted array

Yes, I can implement those in code.

• I have experience in coding and implementing various algorithms and data structures.

• I am proficient in programming languages such as Java, Python, and C++.

• I can provide examples of my previous coding projects upon r...read more

Graph

• Use a graph data structure to represent people as nodes and friend relations as edges

• Each person can be represented as a node with their unique identifier

• Friend relations can be represented as directed edges between nodes

• This allows for efficien...read more

Modify a matrix by setting entire row and column to 1 if an element is 1, then count the number of 1s.

• Iterate through the matrix to find elements with value 1

• Use two arrays to keep track of rows and columns to be modified

• Update the matrix by setting ...read more

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 w...read more

ArrayList is a dynamic array that can store objects of any type. It is used to store and manipulate collections of data.

• ArrayList is part of the System.Collections namespace in .NET.

• It can store objects of any type, including value types and referenc...read more

First in first out (FIFO) is a method of inventory valuation based on the assumption that the first goods purchased are the first goods sold.

• FIFO assumes that the oldest inventory items are sold first

• It is commonly used in industries where the produc...read more

The data structures used for implementing an LRU cache are doubly linked list and hash map.

• Doubly linked list is used to maintain the order of recently used elements.

• Hash map is used for fast lookups to check if an element is present in the cache or ...read more

Autocomplete in IDEs helps developers write code faster by suggesting code snippets and completing code as they type.

• Autocomplete should suggest code snippets based on the context of the code being written

• Autocomplete should prioritize suggestions ba...read more

DSA stands for Data Structures and Algorithms. It is used to efficiently store and manipulate data in computer programs.

• DSA helps in organizing and managing data effectively.

• It provides efficient algorithms for searching, sorting, and manipulating da...read more

Collection is a group of objects while Map is a key-value pair data structure.

• Collection is used to store and manipulate a group of objects.

• Map is used to store and retrieve data based on key-value pairs.

• Collection classes include List, Set, and Queu...read more

A program to print name using an array of strings.

• Declare an array of strings with the name.

• Assign the name to the array.

• Loop through the array and print each string.

Set is a collection of unique elements with no specific order.

• A set can be created using curly braces {} or the set() function.

• Sets can only contain immutable objects like strings, numbers, and tuples.

• Sets are useful for removing duplicates and perfo...read more

Print the level order traversal of binary tree in spiral form

• Perform level order traversal of the binary tree

• Alternate the direction of traversal for each level

• Use a stack to reverse the order of nodes in each level

• Print the nodes in the order of tra...read more

To find and remove a loop in a Linked List, we can use Floyd's Cycle Detection Algorithm.

• Use two pointers, slow and fast, to detect if there is a loop in the Linked List

• If the two pointers meet at some point, there is a loop

• To remove the loop, set on...read more

A code for building a heap and its time complexity

• A heap is a complete binary tree where each node is greater than or equal to its children

• To build a heap, start from the last non-leaf node and heapify down each node

• Time complexity: O(n) for building...read more

Hashtable is not thread-safe while ConcurrentHashmap is thread-safe.

• Hashtable is a legacy class while ConcurrentHashmap is a modern class.

• Hashtable uses synchronized methods while ConcurrentHashmap uses lock striping.

• ConcurrentHashmap allows multiple...read more

Linear Probing in Hashing is a technique to resolve collisions in hash tables by linearly searching for the next available slot.

• Implement a function that takes an array of non-negative integers and returns the corresponding hash table using linear pr...read more