Stack Data Structure
Understanding the Stack Data Structure
A Stack is a linear data structure that follows the Last In First Out (LIFO) principle. The LIFO principle means that the last element added to the stack will be the first element removed from the stack. The last element added to the stack is called the top element.
The basic operations on a Stack are push, pop, peek, is_empty, and size. The push operation adds an element to the top of the stack. The pop operation removes the top element from the stack. The peek operation returns the top element of the stack without removing it. The is_empty operation returns true if the stack is empty and false otherwise. The size operation returns the number of elements in the stack.
Complexity Analysis
A stack can have the following complexities, however its performance is dependent on the underlying data structure used to implement it:
| Case | Time Complexity | Space Complexity |
|---|---|---|
| Best Case | Ω(1) | Ω(n) |
| Average Case | Θ(1) | Θ(n) |
| Worst Case | O(1) | O(n) |
Stacks are often used in conjunction with other data structures. For example, a stack can be used to reverse a string. If you'd like to write a program that simulates when to use a stack, see LeetCode problem 20: Valid Parenthesis.
Code Implementation
A Stack can be implemented in various programming languages. Below are examples of Stack implementations in Python, C++, Java, and Go:
Note: The implementation is for educational purposes. For production use, consider using built-in data structures provided by your programming language.
When should a Stack be used?
A Stack can be implemented when you need to keep track of the order of elements. For example, a stack can be used to keep track of the order of web pages visited in a browser. A stack can also be used to keep track of the order of function calls in a program.
When should a Stack be avoided?
A Stack should be avoided when you need to access elements in a non-sequential manner. For example, if you need to access the middle element of a stack, you would need to pop all the elements above it. This would be inefficient. In this case, a linked list would be a better choice.