# 76 Data Structures and Algorithms Interview Questions [2022 Prep Guide]

Algorithms and data structures are foundational to computer science. As the scaffold for programming languages, technical school recruiters place an emphasis on algorithm and data structures in interviews .
If you ’ re looking for serve with interview questions in those areas, you ’ ve come to the right topographic point. We ’ ra going to cover all the data structure and algorithm interview questions that you should prepare for in 2022 .

## Entry-Level Data Structure Interview Questions

### What Is a Data Structure?

A data structure is a format for storing data on a computer so that it can be accessed and modified easily .

### What Are the Different Types of Data Structures?

The unlike types of data structures are :

• Arrays: A collection of data values stored sequentially
• Stacks: Last-in-first-out (LIFO) data structures where the element placed last is accessed first.
• Queues: A first-in-first-out data structure.
• Linked lists: A collection of data values stored in a linear order and connected to each other
• Graphs: A data structure in which data values are placed in nodes connected by edges
• Trees: Similar to a linked list, but with data values linked in a hierarchical fashion
• Heaps: A binary tree data structure wherein parent data values can be compared to child data values
• Hash table: A table where each value is assigned a key and then stored, making accessing individual values easy.

### What Are the Benefits of Learning Data Structures?

Studying data structures is a room to tap into the world power of data. Without data structures, you ’ d have a boastfully sum of data that you couldn ’ t well access. When you use datum structures, you can retrieve and manipulate data to excavate insights .

### What Are the Applications of Data Structures?

Data structures can be used to :

• Implement dynamic memory allocation
• Model sets and other collections of data
• Search through large data sets easily
• Modeling networks
• Solving shortest problems

### What Is the Difference Between File Structure and Storage Structure?

A storage structure is a datum structure in the calculator ’ mho memory. A file system is besides a theatrical performance of a data structure, but in the aide memory of a calculator .

### Linear Data Structures vs Non-Linear Data Structures: What Is the Difference?

A linear data structure stores data in a linear sequence. You can only traverse the data structure in that analogue sequence. Arrays and stacks are examples of linear data structures .
Non-linear data structures arrange data in ways that are not analogue. A graph, for exemplar, has nodes which are connected to each other through edges. The relationships between the data values are defined by which nodes are connected through edges, and not by a consecutive arrangement. Trees are besides non-linear data structures .

### What Is an Array?

An align is a datum structure in which data values are stored in contiguous locations in the memory. Every element is given an index, which is its position in the sequence of data values .

### How Can You Store the Elements of a 2D Array in the Memory?

There are two techniques used to store 2D arrays :

• Row-major ordering

All of the rows of the align are stored contiguously in this technique. You start with the first rowing, then move on to the second base, and so away, until the entire align has been stored in the memory .

• Column-major ordering

Under this proficiency, the column of the align are stored contiguously rather of the rows. You start with the inaugural column and move on to the subsequent ones consecutive .

### What Is a Linked List?

A linked list is a linear datum structure, but with data values that are not stored in conterminous memory locations. sol in order to traverse the list, each component of the list is connected to the adjacent one using a pointer .

### Explain Multidimensional Arrays.

The standard array has only one dimension ; data values are arranged linearly. But imagine that you want to transfer elements in a tabular format into an array. Tables have two dimensions, so you would need a planar array to describe it .
Any array that has more than one property is a multidimensional array. A 2D array is the most basic shape of a multidimensional range .

### Are Linked Lists Considered Linear or Non-Linear Data Structures?

Linked lists are linear data structures .

### How Can You Use Linked Lists and Arrays? Give Examples.

A linked number is a linear data structure where datum values are not stored in contiguous memory locations. Image spectator applications can use yoke lists to let users go from one picture to the next in chronological order. These images don ’ t need to be stored in conterminous locations, but each one needs to point to the next so that users can scroll through the album .
Arrays are childlike data structures which store the same types of data values in conterminous locations. Imagine you want to run every day and store your daily distance in a datum social organization. In that subject, you could use an array to store the distance for each day and access former entries easily .

### Do Linked Lists Have Any Advantages Over Arrays?

Yes, yoke lists have a few advantages in comparison with arrays .

• Linked lists offer dynamic storage capacity and can easily accommodate newer values. Arrays are initialized with a particular size and can’t adapt to memory requirements as a result.
• It is easier to insert or delete elements in a linked list since the elements are not stored in contiguous memory locations.

### How Do You Reference All of the Elements in a One-Dimension Array?

An index closed circuit can be used to reference all of the items in a unidimensional array. The loop would start at the first range location and bicycle through all of them one by one. Let ’ s say there are newton elements in an array. In that case, the loop would go from 0 through nitrogen .

### What Are Dynamic Data Structures?

Dynamic data structures are data structures whose size is not fixed. They are an important utility for programmers because, in most situations, you will not know precisely how much memory a particular data structure requires. In that situation, active data structures can be used to add or remove new elements easily .

### Why Is Algorithm Analysis Important?

Algorithm analysis is the procedure of assessing the computational capabilities of a particular algorithm and determining whether it can serve a finical function case. This is important to do before any scheduling project because it prevents unanticipated challenges and gives programmers an idea of what they can achieve with a particular algorithm .

### Explain Doubly-Linked Lists (DLL).

A doubly linked list is a modification of a linked list in which every component points to both the component before it and the component after it. It is easy to navigate a doubly linked list both forwards and backwards for this rationality .
Every submission in a doubly linked list has the be :

• A data field to carry a particular data value
• A link to the previous entry in the list
• A link to the next entry in the list

### What Are the Applications of Doubly Linked Lists?

Any application where you require quick advancing and backward navigation can employ doubly linked lists. Some examples include :

• The actions that you’ve taken in an image editing app can be stored in a doubly linked list to allow for each undo/redo operation.
• More complex data structures like binary trees and hash tables can be constructed using doubly linked lists.
• Search engine results pages can be linked to each other using doubly linked lists.

### Explain Stack Along With Its Applications.

A push-down list is a datum structure in which elements are placed one on top of the other and additions and deletions can occur only at the top. Stacks can be used in the stick to applications :

• A stack can be used in applications where users are enabled to backtrack on previous operations by one step or move forward with a new operation.
• Converting infix expressions into postfix expressions.
• The process of reversing the characters in a string can be completed by placing them in a stack and using the pop operation.

### Define Postfix Expression.

A suffix formulation is a format for arranging operators and operands in which the operators are always placed after the operands. The pursue is an exemplar of a suffix expression :
ab+cd- *
The infix version of this saying is :
( a+b ) * ( c-d )

## Senior-Level Data Structure Interview Questions

### What Do You Mean by Queue? Can You Explain Its Applications?

A queue is a datum social organization which follows the First In First Out ( FIFO ) logic for operations, which means that the foremost component input into the line up is operated on first .
A schedule system is a good example of an application of a line up. Imagine a calculate environment where CPU resources are being shared by multiple people. In that case, the ferment that they want to do can be placed in a queue, with the commands that came inaugural being executed by the queue first gear .

### What Is a Dequeue?

Dequeuing is an operation that can be performed on a queue in which an component at the identical front of the queue is removed or accessed for an process .

### Are Stack and Queue the Same Thing? If Not, Explain Why.

Stacks and queues are different data structures. The key differences between them are :

• Stacks follow a first-in-first-out logic whereas queues employ a last-in-first-out logic.
• You can insert and delete elements only at the top of a stack. On the other hand, elements are added at one end of a queue and deleted at the other.
• Stacks use only one pointer, which is for the top of the stack. Queues need two pointers to address the front of the queue and back of the queue.
• Stacks are mainly used in problems requiring recursion whereas queues are better used in applications that require sequential processing.

### What Is the Process Behind Storing Variables in Memory?

The simplest way to store anything in the calculator ’ second memory is using a varying. A varying represents one part of data, such as a quality or a issue. Variables make it easier to write programmes because you can refer to values by their names and write generic programs or functions that work with any rate .
The way variables are stored depends on the programming linguistic process being used. Some programming languages require declaring variables and others don ’ metric ton. There are sealed programming languages in which variables can alone be of a certain character while others are more flexible .

### How To Implement a Queue Using a Stack?

You can implement a line up using a stack by making either the enqueue or dequeue operation dearly-won. In each case below, we will assume two stacks, s1 and s2. The s1 stack holds the data that we are working with while s2 is for impermanent data storage .

#### Enqueue Method

step 1 : If s1 is empty, then push the first element of the stack into s1 .
dance step 2 : If s1 is not vacate, then push elements one by one into s2. now take the first element and rate it in s1, then take all the elements in s2 and stead it back in s1 .
We ’ ve thus ensured that the foremost component is constantly on clear and all of the other elements follow it .

#### Dequeue Method

You can implement a line up using stacks by making the dequeue process dearly-won in the follow way :
step 1 : If s1 is vacate, then don ’ t execute any operation on the data. Simply return an error message saying that the stack is evacuate .
footfall 2 : If s1 is not evacuate, then take all the elements in that stack and place them in s2 one by one. Remove the beginning element in s2 and move all the elements in s2 into s1 .
By moving all the elements in s1 into s2, we ’ ve managed to reverse the order of the data values. now that the beginning element in the line up is at the top of s2, we can use the pop function to remove it .

### How Can You Implement a Stack Using Queues?

You can implement a smokestack using queues either by making the tug or pop operations dearly-won. here are the algorithm for both methods .

#### Making the Push Operation Costly

We use two queues ( q1 and q2 ) to implement a stack by making the push mathematical process costly .

• We start by moving all the elements from q1 to q2
• Next, enqueue the new element into q1
• Transfer all the elements in q2 back into q1

#### Making the Pop Operation Costly

• Move all elements except the last element from q1 to q2
• Remove the last element that remains in q1
• Move all the elements from q2 back into q1

### What Is the Difference Between Push and Pop Operations?

Push and pop are operations that are conducted on stacks. A press operation adds an chemical element into a stack. On the early hired hand, pop music operations remove elements from the smokestack .

### Which Sorting Algorithm Is Considered the Fastest?

Quicksort is generally considered the fastest sorting algorithm. It has a best case time complexity of O ( normality logarithm newton ) and its time complexity in the worst case is O ( n^2 ). however, it is considered the fastest sorting algorithm because it has an average case time complexity of O ( normality logn ), which is faster than early algorithm .

### What Is Merge Sort and How Is It Implemented?

Merge kind belongs to a class of sorting algorithm known as separate and appropriate approaches. It divides a list of elements into two halves and then recursively applies the unify screen technique on each one-half, and then merges the two after sorting them individually .
The follow is the algorithm for a blend sort .

### Can You Explain the Working of a Selection Sort?

Selection sort follows a bare action to sort a list of elements. To start, the list is divided into two parts. The part on the impart is sorted and the separate on the right is uncategorized. initially, the list is unsorted so only the first element is on the forget .
We then scan the array and find the smallest element. That chemical element is swapped with the first element and becomes region of the classify range. We then repeat this process with the second gear component and therefore on. The stick to persona depicts the serve .

### Define an Asymptotic Analysis of an Algorithm.

An asymptotic analysis determines the mathematical run-time operation of different algorithm. Through asymptotic analysis, we are able to establish the best encase, worst case, and average encase scenarios for algorithm .

### Explain Asymptotic Notations.

The follow notations are used in the asymptotic analysis of algorithm .

#### Big Oh Notation

The big ohio note, O ( n ), describes the amphetamine boundary for the runtime of an algorithm. It frankincense describes the worst case time complexity of an algorithm .

#### Omega Notation

This is the lower oblige, or the best sheath scenario, for an algorithm ’ south running time .

#### Theta Notation

The theta notation combines both the amphetamine and lower bound running time of an algorithm .

### What Is a Hash Table in Data Structures?

A hash table is a datum structure in which data is stored along with an index, which is where the component is stored in the memory. This makes hash tables a distribute like arrays, except the data values are stored along with data on their placement in the memory .

### Can You Use an Object as a Key in HashMap?

Yes, you can use an object as a key in a HashMap.

### Can You Store a Duplicate Key in HashMap?

You can not store a duplicate key in a HashMap .

### How Do Hashmaps Handle Collisions in Java?

Hashmaps handle collisions in Java by using a linked list to record entries that have been placed in the same array location. But from Java 8 onwards, the switch was made to using balance trees for the lapp determination alternatively of linked lists .

### What Is the Time Complexity of Basic Operations Get() and Put() in Hashmap Class?

The get and put operations have a meter complexity of O ( 1 ) in Hashmaps assuming that the key-value pairs are evenly distributed across the align or buckets .

### Explain the Implementation of LRU Cache Using Data Structures.

Two data structures are used to implement an LRU hoard. The inaugural is a queue, which is implemented using a linked tilt. The other is a hashish, which holds the page count as a cardinal and the value of the hash is the address of the corresponding queue node .
If a particular page is referenced and is available in the memory, then the node of the list is detached and is placed at the head of the line up. If a especial page is requested and is not in the memory, then it is brought into the memory .
There are situations in which the queue becomes broad, in which case we remove a node from the back of the queue and add a new one in battlefront .

### Define a Tree Data Structure.

A tree is a hierarchical data social organization in which a central node branches into substitute nodes. Each submarine node can have its own conduct nodes .

### What Are Binary Trees?

A binary tree is a kind of tree implementation in which each node can have, at most, two submarine nodes or children. The two children are referred to as the bequeath child and right child .

### Write a Recursive Function To Calculate the Height of a Binary Tree in Java.

To find the acme of a binary tree, we traverse its duration in a postorder sequence. We then calculate the altitude of the leftover and right subtrees, which we can combine to determine the acme of the entire binary star tree. The trace Java code can be used to achieve that .

### What Is the Maximum Number of Nodes in a Binary Tree of Height K?

The maximal number of nodes in a binary tree of altitude potassium is 2k-1, where k is greater than or equal to 1 .

### Describe the Different Kinds of Tree Traversals for a Binary Search Tree.

There are three ways to traverse a tree. They are :

#### Inorder Traversal

Traverse the tree starting at the left field subtree, then to the rout of the tree, and finishing off at the right subtree .

#### Preorder Traversal

Preorder traversal starts at the root, then moves to the left subtree and finally the right subtree .

#### Postorder Traversal

This involves covering the tree starting from the left field subtree and moving to the right subtree. You then move from the properly subtree to the rout to complete the traversal .

### What Is a Binary Search Tree?

A binary search tree is a special tree execution in which internal nodes store keys greater than the keys in the left subtrees and less than the keys in the right subtrees .

### Is Binary Search Better Than Linear Search?

Yes, binary research is more effective than linear search. It has a time complexity of O ( log newton ) whereas the meter complexity of linear search is O ( normality ) .

### Define an AVL Tree.

An AVL tree is a binary star search corner whose height is self-balancing. This is achieved by designing it so that the remainder in the height of the left subtree and right subtree can never exceed one for any node .

### Explain Graph Data Structures.

A graph is a data structure in which a place of nodes is connected to some or all of the other nodes via edges. As a result, graph are non-linear data structures .

### What Are the Applications of Graph Data Structures?

Graphs can be used in many different scenarios. That includes :

• In map applications, where the intersection of two roads is designated as a node
• Social media applications conceptualize networks of users by assigning each user as a node and their friends as the nodes that they are connected to.
• The Internet can be visualized in terms of a graph, where each page that links to another page has an edge that connects to it in the graph.

### How Do You Represent a Graph?

The two most coarse ways of representing graph is by using adjacency lists and adjacency matrices .
An adjacency matrix is a planar array where each row and column represents a particular vertex of the graph. If there exists an border between any two vertices, then the corresponding entrance in the align is designated by a 1. If not, it is designated by a 0 .
adjacency lists represent graph in the form of an array of linked lists. As you can see in the image below, each node in the graph becomes an index element in a associate list. And each index element is connected to the same nodes as in the graph, but this time in a yoke number .

### How Do You Differentiate Between a Tree and Graph Data Structure?

The comply are the cardinal differences between trees and graph :

• Trees have a root node from which all other nodes originate. Graphs don’t have root nodes.
• The vertices in a graph can have bidirectional connections. There is only a single path between two vertices in a tree.
• The nodes in a graph can connect to themselves, which is not possible in a tree.
• Trees are a hierarchical data structure whereas graphs are flat networks.

### Can You Differentiate Between a B Tree and B+ Tree?

The adopt are the differences between B trees and B+ trees :

• Both the internal and leaf nodes in a B tree have pointers. Only the leaf nodes in a B+ tree have pointers.
• Searching a B+ tree is faster because the keys are always in the leaf nodes. The keys of a B tree are not necessarily in the leaf node and searching takes more time as a result.
• B trees don’t maintain a duplicate of the keys in the tree. B+ trees maintain duplicates of keys.
• The lead nodes of B+ trees are stored in the form of structural linked lists. This is not the case for B trees.

### What Is the Difference Between the Breadth-First Search (BFS) and Depth-First Search (DFS)?

Breadth-first search uses the queue data structure to find the shortest path in a graph. Depth-first search does the lapp thing but using the push-down list datum social organization .

### How Do You Know When To Use DFS Over BFS?

The search methodology you use will depend on the depth of the lymph node you ’ rhenium research. If the node is shallow, then you should use BFS. But if there are a distribute of edges between the source and the node to which the search is being conducted, then you should use DFS .

### What Is Topological Sorting in a Graph?

topological screen is a means of ordering the vertices in a graph. The vertices are ordered in such a way that if there is an edge from vertex v1 to vertex v2, then v1 is placed before v2 in the topological classification order .

### What Is a Heap Data Structure?

A heap is a data structure that is based on trees. Heaps are constructed in such a way that they are arrant binary trees, which means that all the levels are filled and every node is left-justified .

### What Is the Advantage of a Heap Over a Stack?

Heaps allocate memory dynamically, which is why they ’ re more flexible than stacks. You don ’ t need to initialize heaps with a particular memory size. With a bus, you can add elements on the run, and the stack will adapt to the new repositing requirements .

### Can Dynamic Memory Allocation Help in Managing Data?

Yes, moral force memory allotment can help in managing data. It is easier to work with data when it can be assigned to memory locations dynamically .

### What Is a Jagged Array?

A erose align is an array of arrays, which means that it is an array that contains early arrays. The arrays within a jagged array can be of varying lengths .

### What Is the Difference Between Null and Void?

When a variable star is assigned as null, that means that it is an evacuate respect. A void cursor, on the early hand, is a pointer that doesn ’ t have any size initially .

### What Is the Left View of a Binary Tree?

The left view of a binary tree is all the nodes that you visit when you traverse the tree from its leave side .

## Data Structures and Algorithms Interview Questions for Python Users

### What Is the Difference Between a List and a Tuple [In Python]?

In short, lists are mutable ( they can be modified ) while tuples are immutable ( they can not be modified ). Lists are ordered by one central index, while a tuple may hold multiple data types in concert in an index-like form .

### Are Dictionaries or Lists Faster for Lookups?

This question tests your compass of the implications for Python data structures and the algorithm you can implement on crown of them. Lists are slower for lookups : it ’ ll take O ( N ) time since filtering through for a value will require as a worst-case scenario filtering through every measure in the list. Dictionaries are well-knit up with key-value pairs, alike to a hash table. Thus the time to search will be O ( 1 ) arsenic long as you have the right key .

### What Are Three Different Ways of Fetching Every Third Item in a List?

There are three different ways to do this : via a concede function, a list inclusion, or a for loop. All three are demonstrated here .

### Using List Comprehension, Print the Odd Numbers Between 0 and 100.

list comprehensions are a feature in Python that allows us to work with algorithms within the default option list data structure in Python. here, we ’ rhenium looking for odd numbers .

A list inclusion allows us to simplify our range and trickle algorithm so we can pack it into one production line of code. This patch of code returns every element between 0 and 100 if it is divisible by 2 .
You should be prepared to describe the list comprehension in detail and with the mighty notation .

### Write a Regular Expression That Confirms an Email Id Using the Python Reg Expression Module “Re”?

When it comes to Python algorithm, a distribute of the work is normally abstracted by the built-in default data structures or easy methods that can be called in one line. regular expression algorithm, used for filtering through selections of textbook, are often some of the most difficult to grasp. You ’ ll have to get familiar with regular construction rules in Python to be able to write out the answer .

## Data Structures and Algorithms Interview Questions for JavaScript Users

### What Is the Result of “10”+20+30 in JavaScript?

This interview question tests your cognition of JavaScript datum primitives, the data types that can be composed into different data structures in Python. In this font, it ’ s a mix between string and numbers data types. Knowing that the result will be 102030 quite than 60 means that you understand that when a bowed stringed instrument type is invoked with the + operator in JavaScript, the automatic behavior is to turn it into a chain operator .
alone by ensuring that everything that interacts with the + operator is a number or BigInt data type can you ensure that a craved behavior of accession happens .

### What Will Be the Output of the Code Below?

This question tests your cognition of arrays and how they interact with different data types. In this encase, you should understand that the duration of the tree range will still be five, even after the delete function. The erase function merely takes the third index token ( since JavaScript arrays are 0-indexed, this means “ maple ” or the one-fourth chemical element ) and makes it undefined. The distance of the underlie array is still the same, it fair contains an undefined element rather of the string “ maple ” .

### How Do You Add an Element at the Beginning of an Array? How Do You Add One at the End?

You have to use the nonpayment .push ( ) method to add something at the end of an array, while you can use the default .unshift ( ) method to add something at the begin. Knowing this answer helps prove that you understand how arrays basically work .

### What Is the For-In Loop in JavaScript? Give Its Syntax.

The for-in loop is a fundamental separate of iterating through data structures. You should be able to describe its syntax to interviewers without hesitation .

This is the encase for-in loop implementation in JavaScript. You would loop through an align by replacing the object identify with the array name, and then place the firearm of iterative code inside the obstruct .

### What Are Arrow Functions?

Arrow functions are a concise and short way to write functions in ES6 and above. They are a way for you to condense your algorithmic logic. The follow case describes an arrow function which plainly prints “ hello ” in the JavaScript console table .

## Data Structures Interview Questions and Answers [General]

### Introduce Yourself.

Make this answer short and pointed. Talk about your educational background and your expertness as a developer. Include some information on your rage for calculator skill and its applications. Refrain from going into your personal background or interests outside of the job you ’ re lend oneself for, unless you ’ re explicitly asked to .

### What Do You Know About Data Structures?

This is a prospect to talk about what data structures are and why they are integral to any scalable computational projects. Explain what makes them important and how they can guide you as a programmer. You can name a few different data structures but there is no need to go besides deep into the specifics of each .

### Why Did You Opt for a Career in Software Development?

One way to answer this interrogate is to explain how you beginning got interested in software and describe some of the first programs you wrote. then talk about some of the personal projects or candid informant contributions you ’ ve made to illustrate your pastime in the field .

### What Is the Most Challenging Project You Encountered on Your Learning Journey?

Be honest when answering this wonder. start by describing the visualize and what you were trying to achieve. then describe the challenges you faced and your gaps in learning. finish up by explaining how you filled those gaps and completed the project .

### Situational Question Based on the Resume.

here are some questions that might arise based on what ’ s on your resume .
A common wonder is whether you can work with a particular programming lyric despite not having a long ton of experience with it. If you ’ re asked this, reassure recruiters by letting them know that you ’ re an autodidact, and are open to learning fresh things on the job. You can give specific examples of when you ’ ve done that in the by .
Gaps in your resume can besides lead to questions from recruiters. If you do have a gap, then explain it honestly. Most companies don ’ deoxythymidine monophosphate mind a gap in a sum up arsenic long as it ’ s justified .

## Data Structures Interview FAQs

### How Do You Prepare for a Software Engineer/Developer Interview?

It ’ south significant to go over the job description and identify what a company is looking for in a software engineer or software developer. Begin your preparations accordingly. For example, if a job description mentions Python and algorithm, then study both of those topics. Start by working on them broadly and then go over the most common interview questions for them .

### Is Software Development a Good Career?

Software development can be a great career option for several reasons. It is a field that is perennially in eminent need and relatively lucrative. It besides gives you the opportunity to work in many different kinds of industries and roles.

### How Should You Answer “Why Should We Hire You as a Software Developer?” During an Interview?

When recruiters ask this doubt, they ’ re looking to find out whether you ’ re a good fit for the company. You need to show that you understand what the ship’s company does and what your function will be. Make sure that you inquiry the company and know what it offers. If possible, get in touch to a developer in the company to learn about they ’ rhenium work and the polish of the team. Include your findings in your answer and explain why you are the perfect campaigner for the occupation .
Since you’re here…
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#### About Sakshi Gupta

Sakshi is a senior Associate Editor at Springboard. She is a technology fancier who loves to read and write about emerging technical school. She is a capacity seller and has experience working in the amerind and u markets .

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