What Is Stacks in Data Structure?
A stack is a fundamental data structure in computer science that follows the Last-In-First-Out (LIFO) principle. It is an abstract data type that represents a collection of elements with two main operations: push and pop.
How Does a Stack Work?
A stack operates like a physical stack of objects, such as a stack of books. You can only access the topmost item, which is the last item added to the stack.
When you add a new item, it goes on top of the existing items, and when you remove an item, it is always the topmost one.
The Push Operation
The push operation adds an element to the top of the stack. It takes the element as input and places it on top.
The previously topmost element becomes the second-to-top element.
Stack before push: 5 8 12 Push(15) Stack after push: 15 5 8 12
The Pop Operation
The pop operation removes and returns the topmost element from the stack. The second-to-top element becomes the new topmost element.
Stack before pop: 15 5 8 12 Pop() -> Returns: 15 Stack after pop: 5 8 12
Common Applications of Stacks:
- Function Calls: Stacks are used to manage function calls in programming languages. Each function call pushes its context onto the stack, allowing for nested calls and proper execution order.
- Undo/Redo Operations: Stacks are used to implement undo and redo functionalities in applications.
Each operation is pushed onto the stack, allowing users to undo or redo actions in a reverse chronological order.
- Expression Evaluation: Stacks are used to evaluate arithmetic expressions by converting them into postfix or prefix notations. The stack holds operands, and operators are applied based on their precedence.
Stacks can be implemented using various data structures, such as arrays or linked lists. In some programming languages, stacks are provided as built-in data types with predefined operations.
To create a stack using an array or a linked list, you need to define the necessary operations: push, pop, peek (to see the topmost element without removing it), and isEmpty (to check if the stack is empty).
Here’s an example implementation of a stack using an array in Python:
class Stack: def __init__(self): self.stack =  def push(self, item): self.stack.append(item) def pop(self): if not self.isEmpty(): return self.pop() else: return None def peek(self): if not self.stack[-1] else: return None def isEmpty(self): return len(self.stack) == 0
Stacks are an essential concept in computer science and find applications in various domains. Understanding how stacks work and their implementation can greatly enhance your problem-solving skills and algorithmic thinking.
Now that you have a solid understanding of stacks, you can explore more advanced topics like stack-based algorithms or different variations of stacks, such as queues or double-ended queues.