What is a Stack in Data Structure? [2024] 📚

a stack of stacked blue and white plates

Have you ever wondered what a stack is in the context of data structures? Well, you’re in the right place! In this article, we’ll dive deep into the world of stacks, exploring their definition, basic operations, implementations in popular programming languages, time complexity, and applications. By the end, you’ll have a solid understanding of stacks and how they can be used in various scenarios. So, let’s get started!

Quick Answer
Quick Tips and Facts
Background: Understanding the Stack Data Structure
LIFO Principle: Last In First Out
Basic Operations of a Stack
Working of a Stack Data Structure
Stack Implementations in Python, Java, C, and C++
Time Complexity of Stack Operations
Applications of the Stack Data Structure
FAQ
Conclusion
Recommended Links
Reference Links

Quick Answer

In simple words, a stack is a linear data structure that follows the Last In First Out (LIFO) principle. It can be visualized as a pile of plates, where the last plate added is the first one to be removed. Stacks are widely used in programming and have various applications in different domains.

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Quick Tips and Facts

A stack is a collection of elements with two main operations: push and pop.
The push operation adds an element to the top of the stack, while the pop operation removes the topmost element.
Stacks can be implemented using arrays or linked lists.
The topmost element in a stack is the one that was added most recently.
Stacks are used in many real-life scenarios, such as browser history, function call stack, and undo/redo functionality.

Now that we have a quick overview, let’s dig deeper into the background and workings of the stack data structure.

Background: Understanding the Stack Data Structure

person holding pencil near laptop computer

To truly grasp the concept of a stack, let’s imagine a real-life scenario. Picture a stack of plates in a buffet restaurant. When you add a plate to the stack, you place it on top of the existing plates. Similarly, when you remove a plate, you take it from the top of the stack. This Last In First Out (LIFO) principle is the core idea behind a stack data structure.

In programming, a stack is a collection of elements that supports two fundamental operations: push and pop. The push operation adds an element to the top of the stack, while the pop operation removes the topmost element. Additionally, stacks often provide other operations like isEmpty (to check if the stack is empty), isFull (to check if the stack is full), and peek (to get the value of the top element without removing it).

1. LIFO Principle: Last In First Out

Video: The Power of Last-In-First-Out: Understanding the Stack Data Structure with Real-World Examples.

The LIFO principle is the defining characteristic of a stack. It means that the last element added to the stack is the first one to be removed. Just like the plates in our buffet restaurant analogy, the most recently added plate is the first one you can take.

This principle is crucial in many scenarios. For example, when you press the “undo” button in a text editor, the most recent action is reversed first. Similarly, when you navigate through web pages using the back button, you go back to the previously visited page.

2. Basic Operations of a Stack

Video: Introduction to Stacks.

As mentioned earlier, a stack supports two primary operations: push and pop. Let’s take a closer look at these operations:

Push: The push operation adds an element to the top of the stack. It increases the stack’s size by one and places the new element at the top.
Pop: The pop operation removes the topmost element from the stack. It decreases the stack’s size by one and returns the removed element.

In addition to push and pop, stacks often provide other operations:

isEmpty: This operation checks if the stack is empty. It returns true if the stack has no elements, and false otherwise.
isFull: This operation checks if the stack is full. It is relevant when using an array-based implementation with a fixed size.
Peek: The peek operation returns the value of the top element without removing it from the stack.

3. Working of a Stack Data Structure

Video: Learn Stack data structures in 10 minutes .

To understand how a stack works internally, we need to explore its implementation. Stacks can be implemented using arrays or linked lists. Let’s take a closer look at each implementation:

Array-based Implementation: In this approach, a stack is represented using an array. We use a pointer called TOP to keep track of the top element. Initially, when the stack is empty, the value of TOP is set to -1. When we push an element, we increment TOP and add the new element at the index pointed by TOP. When we pop an element, we return the element at the index pointed by TOP and decrement TOP.
Linked List-based Implementation: In this approach, a stack is implemented using a linked list. Each node in the linked list represents an element in the stack. The top of the stack is represented by the head of the linked list. When we push an element, we create a new node and make it the new head of the linked list. When we pop an element, we remove the head node and update the head to the next node in the list.

4. Stack Implementations in Python, Java, C, and C++

Video: Stacks And Queues In Data Structure | Data Structures And Algorithms Tutorial | Simplilearn.

Stacks can be implemented in various programming languages, including Python, Java, C, and C++. Let’s explore how stacks are implemented in each of these languages:

Python: In Python, stacks can be implemented using lists. The append() method is used to push elements onto the stack, and the pop() method is used to remove elements from the stack.
Java: In Java, stacks can be implemented using the Stack class from the java.util package. The push() method is used to push elements onto the stack, and the pop() method is used to remove elements from the stack.
C: In C, stacks can be implemented using arrays. The push() function is used to push elements onto the stack, and the pop() function is used to remove elements from the stack.
C++: In C++, stacks can be implemented using the std::stack container from the Standard Template Library (STL). The push() function is used to push elements onto the stack, and the pop() function is used to remove elements from the stack.

5. Time Complexity of Stack Operations

Video: Stack : Time complexity analysis of all Stack operations | Stack Data Structure Playlist.

The time complexity of stack operations is an important consideration when using stacks in your programs. Let’s take a look at the time complexity of the basic stack operations:

Push: The push operation has a constant time complexity of O(1) for both array-based and linked list-based implementations. This is because adding an element to the top of the stack only requires updating the TOP pointer or modifying the linked list’s head.
Pop: The pop operation also has a constant time complexity of O(1) for both array-based and linked list-based implementations. Similar to the push operation, removing the topmost element only requires updating the TOP pointer or modifying the linked list’s head.

6. Applications of the Stack Data Structure

Video: Stacks Applications.

Stacks have a wide range of applications in various domains. Here are a few examples:

Reversing a Word: Stacks can be used to reverse the order of characters in a word. By pushing each character onto a stack and then popping them off, we can obtain the reversed word.
Compilers: Compilers use stacks to implement the function call stack. When a function is called, its return address and local variables are pushed onto the stack. When the function returns, the return address is popped from the stack, and the program continues execution from that point.
Browsers: Browsers use stacks to implement the back and forward navigation functionality. Each visited page is pushed onto a stack, allowing users to navigate back to previously visited pages by popping them off the stack.

These are just a few examples of how stacks are used in real-world scenarios. Their simplicity and efficiency make them a valuable tool in many programming applications.

FAQ

green-and-brown birds perching on tree

What is a stack in simple words?

In simple words, a stack is a data structure that follows the Last In First Out (LIFO) principle. It can be visualized as a pile of plates, where the last plate added is the first one to be removed.

What is stack and queue?

A stack and a queue are both data structures used to store and manipulate collections of elements. The main difference between them is the order in which elements are accessed. In a stack, the last element added is the first one to be removed (LIFO), while in a queue, the first element added is the first one to be removed (FIFO).

What is the purpose of the stack?

The purpose of a stack is to provide a simple and efficient way to store and retrieve elements. It is often used in scenarios where the order of access is important, such as function call stacks, browser history, and undo/redo functionality.

Is stack a good data structure?

Yes, a stack is a good data structure for many applications. Its simplicity and efficiency make it a valuable tool in various programming scenarios. However, it’s important to choose the appropriate data structure based on the specific requirements of your application.

Conclusion

brown and black bird on green plant

In conclusion, a stack is a fundamental data structure that follows the Last In First Out (LIFO) principle. It provides efficient operations for adding and removing elements, making it a valuable tool in many programming scenarios. Whether you’re reversing a word, implementing a compiler, or building a browser, understanding stacks is essential.

So, the next time you encounter a problem that requires managing elements in a Last In First Out manner, consider using a stack. It’s a powerful tool that can simplify your code and improve its efficiency.

Now that you have a solid understanding of stacks, why not explore more programming languages and game development topics on Stack Interface™? You’ll find a wealth of knowledge to help you level up your skills!