Top 100 Data Structures and Algorithms Interview Questions 2023

Data structures are the key building blocks of every computer program as they allow you to organize and manipulate data in an efficient way. Arrays, stacks, queues and linked lists are examples of data structures.

Data structures are used in many fields and they help to reduce time spent on operations and improve efficiency and reuse. They are also integral to scalable computational projects.

Arrays

Arrays are data structures that store a series of similar types of elements in continuous memory locations. They can be accessed using an index value that starts at zero and increases to the element’s actual location in memory.

Often, the array is used in cases where a program needs to define and store different types of data. For example, if you need to define the names of students in a class, it is more convenient to store them in an array instead of creating multiple variables to hold them.

In addition to being a useful data structure, arrays also work extremely well when you need to access multiple values in adjacent memory locations. This is because arrays use a grid structure that lets you visualize your computer’s memory as an assortment of small elements, like squares.

When you create an array of a certain size, all of the space that is “reserved” in memory will be kept empty until you insert additional values. This ensures that all the values you add to the array will be stored in adjacent memory locations until you need them, which is a very efficient way of organizing information in your computer’s memory.

Once you have created an array, you can’t change its size. Adding or deleting elements from an array is expensive because you need to allocate a new array and copy the elements from the old one into it.

In addition to being a very valuable data structure, arrays are also used in many other data structures, including stacks and queues. It’s essential to know how these structures work and how to implement them in your code. These data structures are fundamental to understanding the basics of coding and programming, so it’s important to learn them thoroughly.

Stacks

Data structures are used to store data in a computer so that it can be accessed easily. The different types of data structures include arrays, linked lists, stacks, queues, trees, graphs, and hash tables.

Stacks are linear data structures that hold a sequential sequence of elements. They are an Abstract Data Type (ADT) that supports push and pop operations.

They work on the last-in, first-out (LIFO) process, which means that the last element added will be the last element removed. This is different from arrays, which do not follow a particular order. Stacks are important to understand in Top 100 Data Structures and Algorithms Interview Questions 2023 as they are essential for solving problems that require recursion.

A stack consists of an ordered sequence of data elements, with each element arranged in a descending order. The structure is accessed by using a pointer to the top of the stack, which identifies the last element to be inserted.

To add an element to the stack, we need to use the push operation. Similarly, to remove an element from the stack, we need to use the pop operation.

Stacks can be implemented as either an array or a linked list. In either case, they allow push and pop operations without other helper functions.

The basic operations of a stack are push and pop, but some implementations provide additional operations such as size (the number of data elements on the stack) and peek (looking at the top element without removing it). These non-essential operations can be useful in implementing algorithms such as depth-first search.

Stacks are one of the most commonly used data structures in computer science. They can be found in a wide variety of applications, from storing local variables to maintaining a playlist in media players. Stacks are also used in many other areas of programming, including depth-first search, sorting, and graph data structures.

Queues

A queue is a data structure that is used to store a collection of elements. It can be a single-ended queue or a double-ended queue. In a standard queue, new elements are inserted at one end and old elements are removed from the other.

This is called a First-In-First-Out (FIFO) data structure. This means that the element added last should be accessed first, and the elements inserted first should be accessed last.

In order to maintain the ordering of a queue, it is necessary to have a pointer to the front and a pointer to the rear, which indicate the elements at the front and at the back of the queue, respectively. These pointers can be stored in a list of arrays or linked lists.

Using a fixed-length array is limited in capacity, so it is important to avoid storing items too close to the head of the queue. By turning a fixed-length array into a circular queue, this can be avoided.

The key advantage of this approach is that a circular queue can be implemented with a fixed number of elements and does not require any memory to be used for storing the queue’s contents. This makes it ideal for applications where data must be able to be accessed quickly.

For example, queues are commonly used in operating systems to handle interrupts. They are also used in printers to ensure that pages are printed in the correct order.

A priority queue is a special type of queue that is used to store and retrieve data with the highest priority. It is often referred to as a ring buffer as it forms a circle-like structure by connecting the nodes end-to-end.

Hash Tables

A hash table is a type of data structure that uses a hash function to map keys and values. Hash tables are useful for storing data in an associative way, and they can be used to search and retrieve data quickly.

Hash tables are often used to store text, but they can also be used to store data for other types of applications. They are fast and efficient, so they are used in many different kinds of software.

In a hash table, each key has a unique index value. This makes it possible to locate an element quickly, regardless of the size of the data.

As a hash table grows, it can be resized to spread the entries further apart. Its size is typically determined by a threshold value. For example, a hash table with a threshold of 0.6 would resize when 60% of the space is occupied.

One drawback to hash tables is that they can sometimes collide, or create a duplicate index for more than one key. This is called a hash collision and it can cause performance problems.

When a hash table is full, it can be more effective to use an alternative technique called separate chaining. This method stores each bucket on a linked list, which is associated with the key.

However, this increases the time needed for a lookup in the hash table, because each bucket must be traversed to find the entry it needs. This is compared to linear probing, which does not involve traversing each link and can be faster.

A hash table is a very important data structure that helps in storing data and making it easy to access. It is also an essential part of programming. Tech recruiters place an emphasis on algorithms and data structures in interviews, so it’s important for programmers to understand them well.

Graphs

Graphs are data structures that represent a space of objects in a way that allows users to visualize the relationships among those objects. They are made up of vertices (nodes) and edges, which are lines or arcs that connect any two nodes in the graph.

Using graphs to analyze data is a useful technique, as it helps people easily understand the relationships between numbers and information. Moreover, graphs are often used to show trends or patterns, and can be compared with other data.

Line graphs are one of the most common types of graphs. They display numerical data in a visual format, and can be arranged horizontally or vertically. They can also display more than one group of data at once.

Bar graphs are another type of graph that is commonly used in data analysis. They are usually used to compare a large number of factors, such as age, gender, income, and racial background. Stacked bar graphs are a great option for displaying multiple trends in a single chart.

Pie charts are a type of graph that displays different data sets in an interesting manner. They can be used to compare the number of children in a school, or the amount of money that goes toward public education.

Similarly, stacked bar graphs can be used to display how much money is spent on different programs, or how many people are in a specific industry. They can also be used to show how the size of a company changes over time.

When choosing a graph, it’s important to consider what kind of data you want to analyze and how your audience will best interpret your findings. In addition, it’s important to choose the right format for your graph. Using the wrong graph type can lead to inefficient results and confusing users.