Which data structures are asked in interviews?

As a software engineer preparing for coding interviews, knowing which data structures are commonly asked about is key to your success. Having a solid understanding of data structures like arrays, linked lists, trees, graphs, stacks, queues, heaps, and hash tables will ensure you are ready to tackle a wide range of technical questions.

Why Review Data Structures for Interviews?

There are several reasons reviewing data structures is crucial when prepping for the coding portions of interviews:

• Data structures form the foundation of good software design and architecture. Interviewers want to assess your skills in structuring and organizing data in efficient ways.
• Questions about data structures test your algorithms knowledge and problem-solving abilities. You may be asked to select the best data structure for a given scenario or implement operations like search, insert, and delete.
• Understanding when and why to use built-in data structures vs implementing your own is key. The standard library provides excellent implementations – knowing how to utilize them effectively demonstrates your experience.
• Data structures questions come up frequently. Array and string manipulation, tree traversal, graph search – these topics account for a significant portion of coding interview questions.
• Data structures demonstrate your technical breadth. Showing competency across a variety of data structures illustrates the well-roundedness companies want.

In short, data structures questions allow interviewers to thoroughly evaluate your skills as a software engineer. A strong data structures foundation is what makes passing the coding interview achievable.

Most Frequently Asked Data Structures

While there are dozens of data structures studied in computer science, some come up more often than others in coding interviews. Here are 8 essential data structures to review:

Arrays

Arrays allow storing a fixed-size sequential collection of elements. They are one of the most commonly used data structures due to their ease of use and efficiency. In interviews, expect array questions involving:

• Searching/accessing elements
• Insertion and deletion
• Reversing/rotating
• Sorting elements

Linked Lists

Linked lists consist of nodes storing data with pointers to other nodes. They allow for efficient insertion and deletion, but lack random access. Interview questions may involve:

• Singly vs doubly linked lists
• Reversing a linked list
• Detecting loops
• Merging two linked lists

Stacks

Stacks operate in a last in, first out (LIFO) manner. Addition and removal of elements takes place at one end. Interview questions focus on:

• Using a stack to check for balanced parentheses
• Implementing stacks with arrays vs linked lists
• Stack operations like push(), pop(), isEmpty(), etc.

Queues

Queues follow first in, first out (FIFO) ordering. Elements are inserted at the back and removed from the front. Key interview topics include:

• Implementing queues with arrays vs linked lists
• Circular queues
• Priority queues
• Queue operations like enqueue(), dequeue(), isEmpty(), etc.

Trees

Trees consist of nodes connected by edges in a hierarchical structure. Common interview tree questions involve:

• Binary trees – full, complete, balanced
• Binary search trees – inserting, searching, deletion
• Tree traversal – preorder, inorder, postorder, BFS, DFS
• Tries (prefix trees)
• Heaps (min-heaps, max-heaps)

Graphs

Graphs model pair-wise connections between objects using vertices/nodes and edges. Interview graph questions test your skills in:

• Directed vs undirected graphs
• Adjacency matrix vs adjacency list
• Graph search – breadth-first search, depth-first search
• Shortest path algorithms – Dijkstra’s, Bellman-Ford, Floyd-Warshall

Hash Tables

Hash tables store key-value pairs for efficient lookup and insertion. Interview topics focus on:

• Implementing hash functions
• Collision resolution – chaining, linear probing
• Resizing hash tables when full
• Time and space complexity

Types of Data Structures Interview Questions

Data structures questions generally fall into several categories:

Implementation

You may be asked to implement a particular data structure like a hash table or binary search tree from scratch. This tests your understanding of how the core data structure functions.

Prediction

You may be provided with a data structure (e.g. an array) and need to predict what will happen when a certain operation is applied or what the state will be after a sequence of operations.

Optimization

Given a data structure (like a linked list), you may need to optimize it for space or time efficiency. For example, redesigning node storage to use less memory.

Selection

You may need to pick the most optimal data structure for a given scenario. Or select certain methods or techniques to optimize performance.

Coding Algorithms

Common data structure operations like search, sort, insert, delete, traverse are frequently asked to implement. You may code up BST insertion or hash table resizing for instance.

So in summary, be ready for a blend of conceptual questions and writing actual code snippets related to data structures.

How to Effectively Prepare for Data Structure Interview Questions

Here are some tips to ace data structures interview questions:

• Review theory comprehensively – Know the fundamentals of how each data structure works and when it’s most applicable.
• Implement key data structures – Practice coding up arrays, linked lists, trees, etc from scratch.
• Memorize time/space complexity – Be familiar with the runtime and memory tradeoffs of different implementations.
• Study common algorithms – Sorting, searching, traversal – know how they work and their computational efficiency.
• Practice coding challenges – Leetcode, HackerRank and other platforms have great data structure problems to drill.
• Learn built-in libraries – Know when to use the native data structures and collections classes.
• Review before interviews – Refresh core concepts and algorithms right before going in.

Gaining mastery of key data structures takes time and dedication. But it’s one of the most valuable investments you can make in acing the coding interview.

Conclusion

Data structures form the basis of good software engineering practices. They establish the foundation for designing efficient, performant systems. That’s why they feature so prominently in coding interviews.

Be prepared to demonstrate your knowledge across a variety of data structures. The most frequently asked include arrays, linked lists, stacks, queues, trees, graphs, and hash tables. Questions run the gamut from theoretical to coding algorithms to selecting optimal implementations.

Review core concepts, practice implementing data structures, solve coding challenges, learn standard libraries and prepare thoroughly. With strong data structures knowledge, you’ll confidently tackle a major portion of coding interview questions.