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Ranjan Kumar
Updated on 21st June, 2024 , 9 min read
DSA Interview Questions: Top DSA Questions asked in tech Interviews
DSA Interview Questions
This article will answer the most asked Data Structure Interview Questions so you know what to expect in the interview.
You might be wondering what questions you’ll get in your next data structure interview. Just remember data structure interviewers aren’t trying to trick you and don’t expect perfection, but it’s their chance to test you before they invest in you. Always prepare well.
Data structure and algorithm questions are a part of any programming job interview, especially for Data Science and Java based roles. Having sound knowledge of data structures and algorithms will set you apart from the crowd. The following Data Structure interview questions will help you crack your next interview!
Basic DSA Interview Questions for Freshers
What is Data Structure
Data Structure is the way data is stored and manipulated for retrieval and access. It also defines how different set of data are related to each other and forms algorithms.
What are the Data Structures?
Here are the types of data structures:
Lists: A collection of related things linked to previous or/and next data items.
Arrays: A collection of same type of values.
Records: A collection of fields, each of which contains single data type.
What is Linear Data Structure? Give few examples.
A data structure is said to be linear if all its elements or data items are arranged in a sequence or in linear order. The elements are stored in non-hierarchical way so that each item has successors and predecessors except the first and last element in the list. Examples of linear data structures are Arrays, Stack, Strings, Queue, and Linked List.
What are the applications of Data Structures?
Numerical analysis, Operating System, AI, Compiler design, Database management, Graphics, Statistical analysis, Simulation.
What is the difference between file structure and storage structure?
The difference lies in the memory area accessed. Storage structure refers to the data structure in the memory of the computer system, whereas file structure represents the storage structure in the auxiliary memory
What is a multidimensional array?
A multidimensional array is a multidimensional array with more than one dimension. It is an array of arrays or an array with numerous layers. The 2D array, or two-dimensional array, is the most basic multidimensional array. As you'll see in the code, it's technically an array of arrays. A 2D array is also referred to as a matrix or a table with rows and columns. Declaring a multidimensional array is the same as saying a one-dimensional array. We need to notify C that we have two dimensions for a two-dimensional array.
How are the elements of a 2D array stored in the memory?
Row-Major Order: -In row-major ordering, all of the rows of a 2D array are stored in memory in a contiguous manner.
First, the first row of the array is entirely stored in memory, followed by the second row of the array, and so on until the final row.
Column-Major Order: In column-major ordering, all of the columns of a 2D array are stored in memory in the same order. The first column of the array is entirely saved in memory, followed by the second row of the array, and so on until the last column of the array is wholly recorded in memory.
What is a linked list Data Structure?
It’s a linear Data Structure or a sequence of data objects where elements are not stored in adjacent memory locations. The elements are linked using pointers to form a chain. Each element is a separate object, called a node. Each node has two items: a data field and a reference to the next node. The entry point in a linked list is called the head. Where the list is empty, the head is a null reference and the last node has a reference to null.
A linked list is a dynamic data structure, where the number of nodes is not fixed, and the list has the ability to grow and shrink on demand.
It is applied in cases where:
- We deal with an unknown number of objects or don’t know how many items are in the list
- We need constant-time insertions/deletions from the list, as in real-time computing where time predictability is critical
- Random access to any elements is not needed
- The algorithm requires a data structure where objects need to be stored irrespective of their physical address in memory
- We need to insert items in the middle of the list as in a priority queue
- Some implementations are stacks and queues, graphs, directory of names, dynamic memory allocation, and performing arithmetic operations on long integers.
What is a doubly linked list? Give some examples.
It is a complex type (double-ended LL) of a linked list in which a node has two links, one that connects to the next node in the sequence and another that connects to the previous node. This allows traversal across the data elements in both directions.
Examples include:
- A music playlist with next and previous navigation buttons
- The browser cache with BACK-FORWARD visited pages
- The undo and redo functionality on a browser, where you can reverse the node to get to the previous page
What are dynamic Data Structures? Name a few.
They are collections of data in memory that expand and contract to grow or shrink in size as a program runs. This enables the programmer to control exactly how much memory is to be utilized. Examples are the dynamic array, linked list, stack, queue, and heap.
Why do we need to do an algorithm analysis?
A problem can be solved in more than one way using multiple solution algorithms. Algorithm analysis gives an estimate of the resources required by an algorithm to solve a particular computational problem. Time and space resources required to run are also determined.
Time complexity of an algorithm measures the time taken by an algorithm to run as a function of the size of the input. Space complexity measures the space or memory required by an algorithm to run as a function of the size of the input.
What is a stack?
A stack is an abstract data type that is a linear data structure like a real physical stack or piles where you can only take the top item off the stack to remove things. So insertion (push) and deletion (pop) happen only at one end called top of the stack with a particular order: LIFO (Last In First Out) or FILO (First in Last Out).
DSA Interview Questions for Experienced
What is a postfix expression?
A postfix expression is made up of operators and operands, with the operator coming after the operands. That is, in a postfix expression, the operator comes after the operands. Likewise, what is the proper postfix form? The correct postfix phrase is A B + C *.
What is a queue Data Structure?
In this type of data structure interview questions, you can also discuss your experience and situations using queue. A queue is an abstract data type that specifies a linear data structure or an ordered list, using the First in First Out (FIFO) operation to access elements. Insert operations can be performed only at one end called REAR and delete operations can be performed only at the other end called FRONT.
What are the advantages of heap over stack?
In this data structure interview questions, try to give various advantages along with examples if possible. It will show the interviewer your domain expertise. Both heap and stack are part of memory and used in Java for different purposes:
- Heap is more flexible than stack because memory can be dynamically allocated and deallocated as needed
- Heap memory is used to store objects in Java, stack memory is used to store local variables and function call
- Objects created in heap are visible to all threads, variables stored in stack are only visible to the owner as private memory
- When we use recursion, heap memory size is more whereas stack memory gets filled up quickly
Which algorithm is the fastest? Why?
One algorithm can’t be the best, as each algorithm is designed for a specific data structure and data set. But QuickSort is generally the fastest as it’s the best for most inputs.
Advantages over other algorithms:
- Cache friendly: It linearly scans and linearly partitions the input. We can make the most of every cache load.
- Can skip some swaps: QuickSort is slightly input sensitive and can skip some swaps.
- Works well even in worst case input sets as the order is generally random.
- Easy to adapt to already or mostly sorted inputs.
- When speed matters more than stability.
What is the merge sort? How does it work?
Merge sort is a divide-and-conquer algorithm for sorting the data. It works by merging and sorting adjacent data to create bigger sorted lists, which are then merged recursively to form even bigger sorted lists until you have one single sorted list.
How does the Selection sort work?
This is one of the most frequently asked data structure interview questions. Selection sort works by repeatedly picking the smallest number in ascending order from the list and placing it at the beginning. This process is repeated moving toward the end of the list or sorted subarray.
Scan all items and find the smallest. Switch over the position as the first item. Repeat the selection sort on the remaining N-1 items. We always iterate forward (i from 0 to N-1) and swap with the smallest element (always i).
Time complexity: best case O(n2); worst O(n2)
Space complexity: worst O(1)
What is an asymptotic analysis of an algorithm?
Asymptotic analysis is the technique of determining an algorithm's running time in mathematical units to determine the program's limits, also known as "run-time performance." The purpose is to identify the best case, worst case, and average-case times for completing a particular activity. While not a deep learning training technique, Asymptotic analysis is an essential diagnostic tool for programmers to analyze an algorithm's efficiency rather than its correctness.
What are the advantages of binary search over a linear search?
In a sorted list:
- A binary search is more efficient than a linear search because we perform fewer comparisons. With linear search, we can only eliminate one element per comparison each time we fail to find the value we are looking for, but with the binary search, we eliminate half the set with each comparison.
- Binary search runs in O(log n) time compared to linear search’s O(n) time. This means that the more of the elements present in the search array, the faster is binary search compared to a linear search.
Differentiate NULL and VOID
Null is a value, whereas Void is a data type identifier Null indicates an empty value for a variable, whereas void indicates pointers that have no initial size Null means it never existed; Void means it existed but is not in effect
Do dynamic memory allocations help in managing data? How?
Dynamic memory allocation stores simple structured data types at runtime. It has the ability to combine separately allocated structured blocks to form composite structures that expand, and contract as needed, thus helping manage data of data blocks of arbitrary size, in arbitrary order.
How do you find the height of a node in a tree?
The height of the node equals the number of edges in the longest path to the leaf from the node, where the depth of a leaf node is 0.
What are the differences between the B tree and the B+ tree?
The B tree is a self-balancing m-way tree, with m defining the tree's order. Depending on the number of m, B tree is an extension of the Binary Search tree in which a node can have more than one key and more than two children. The data is provided in the B tree in a sorted manner, with lower values on the left subtree and higher values on the right subtree.
The B+ tree is an advanced self-balanced tree since every path from the tree's root to its leaf is the same length. The fact that all leaf nodes are the same length indicates that they all occur at the same level. Specific leaf nodes can’t appear at the third level, while others appear at the second level.
Conclusion
These DSA interview questions would give you an insight into what kind of questions could be asked. Although you can expect many of these data structure interview questions, you also need to invest some time into your learning curve. A good understanding of basic data structures and how to access elements from an array or linked list, or coding for data science, is equally important.
A key component of the technical interview process is understanding data structures, particularly for candidates hoping to succeed as Java full stack engineers. Having a solid understanding of concepts such as arrays, linked lists, trees, and graphs can greatly enhance your ability to solve problems and write more efficient code
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Frequently Asked Questions
Which algorithm is generally the fastest?
QuickSort is generally the fastest for most inputs due to its efficiency and adaptability to various data sets.
What are data structures?
Data structures are ways to store and organize data to enable efficient access and modification. Examples include arrays, linked lists, stacks, and queues.
What is a linked list?
A linked list is a linear data structure where elements are stored in nodes, each containing data and a reference to the next node. It allows for efficient insertion and deletion.
What is a stack?
A stack is a linear data structure that follows the Last In, First Out (LIFO) principle, where elements are added and removed from the same end, called the top.
What are the advantages of binary search over linear search?
Binary search is more efficient, with a time complexity of O(log n), compared to linear search's O(n), as it halves the search space with each step.