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Top Data Structure & Algorithms Interview Questions


You might be curious about the types of questions you'll be asked during your next data structure interview. Just keep in mind that data structure interviewers aren't attempting to fool you, and they don't expect perfection, but it is their chance to assess your understanding before investing in your job.

Any programming job interview, especially one for a Data Science or Java-based post, should include data structures and algorithm questions. Knowing how to think in terms of data structures and algorithms will help you stand out from the crowd. Data structures might be the subject of a few or many questions in every programming language interview. Here are some of the most common data structure interview questions and answers, along with their replies:

1. What is the definition of a data structure?

The Data Structure describes how data is organized (stored), altered, and accessed. It also establishes relationships and forms algorithms by defining how distinct types of data relate to one another.

2. What are the differences between linear and non-linear data structures?

Linear: If the elements of a data structure form a sequence or a linear list, it is said to be linear. The array is an example. Stacks, Queues, and Linked Lists

Non-Linear: If the traversal of nodes is nonlinear, the data structure is said to be non-linear. Graphs and Trees are two examples.

3. What is the definition of an array?

Arrays are collections of comparable sorts of data kept in close proximity in memory. It is the most basic data structure in which a data element can be accessed at random using its index number alone.

4) What is the definition of a stack?

A stack is an ordered list in which only one end, called the top, can be used for insertion and deletion. It's a recursive data structure with a top-level pointer. The stack is also known as a Last-In-First-Out (LIFO) list because the piece that is entered first in the stack is deleted last.

5) What is the difference between PUSH and POP?

The PUSH and POP actions define how data in a stack is saved and retrieved.

  • PUSH: This command indicates that data is being "inserted" into the stack.
  • POP: POP is a data retrieval protocol. It denotes the removal of data from the stack.

6) What is a queue? How is it different from a stack?

A queue is a type of linear structure that accesses elements in the FIFO (First In First Out) order. The basic operations on a queue are dequeue, enqueue, front, and back. A queue, like a stack, can be built with arrays and linked lists.

The item that was most recently added to a stack is removed first. In the event of a queue, however, the item that was most recently added gets removed first.

7) Could you please explain what you mean by FIFO and LIFO?

Both FIFO and LIFO are methods for accessing, storing and retrieving data structure elements. Last In First Out (LIFO) is an acronym meaning Last In First Out. The most recently stored data is extracted first in this method.

First In First Out is abbreviated as FIFO. The data that has been stored the least recently will be extracted first using this method.

8) Could you please explain tree traversal?

Tree traversal refers to the process of visiting all of a tree's nodes. It always begins at the root node, and there are three methods for doing so:

  • Traversal in order
  • Traversal is now available for pre-order.
  • Traversal once an order has been placed

9) Could you explain the difficulty with the Hanoi Tower?

The Tower of Hanoi is a mathematical puzzle consisting of three towers (or pegs) and multiple rings. Each ring has a different size and is layered on top of one another, with the larger ring being beneath the smaller.

The purpose of the Tower of Hanoi issue is to shift the disk's tower from one peg to the next while maintaining its features.

10) How does an array's selection sort work?

The selection sort is a simple sorting algorithm, although it isn't always efficient. The smallest element is located first and exchanged with the element at subscript zero, resulting in the smallest element being placed first.

The subarray's smallest element is then moved next to subscripts 1 through n-1 and swapped with the element at subscript 1, putting the second smallest element in the second position. The stages are continued until the last element is reached.

11) What is an algorithm and why is it necessary to do an algorithm analysis?

An algorithm is a way of solving a problem or manipulating data that follows a set of steps. It specifies a series of instructions that must be carried out in a specific order to get the desired result.

Several solution algorithms can be used to solve a problem in more than one way. Algorithm analysis estimates the resources required by an algorithm to solve a certain computer task. It's also decided how much time and space are needed to complete the task.

12) What is the meaning of a postfix expression?

Operators and operands make up a postfix expression, with the operator coming after the operands. The operator comes after the operands in a postfix expression. What is the right postfix form, too? A B + C * is the correct postfix phrase.

13) In DSA, what is a heap?

A heap data structure is a complete binary tree with a predetermined order. There are two types of heaps:

Max Heap and Minimum Heap

14) What operations are possible with stacks?

  • push() - Adds a new element to the stack's top.
  • pop() - Removes an element from the stack's top.
  • peek() - Shows the element at the top of the stack.

This concludes the top data structure interview questions. These Data Structure interview questions can provide you with an idea of the types of questions you might be asked. Although you may be able to answer many of these data structure interview questions, you must devote some time to enhance your knowledge of DSA. 

To learn Data Structures in detail, check our Data Structures Certification course designed and presented by Google Developer.