Python Data Structure: Stack

A stack is a linear data structure that stores ordered items with a specific access rule: items can only be added or removed from the top of the stack. This behaviour follows the LIFO (Last In, First Out) principle, meaning the last item added is the first to be removed.

By imposing these restrictions on how we interact with data, stacks ensure that certain operations are highly efficient.

Python Data Structure: Stack

A stack is a linear data structure that stores ordered items with a specific access rule: items can only be added or removed from the top of the stack. This behaviour follows the LIFO (Last In, First Out) principle, meaning the last item added is the first to be removed.

By imposing these restrictions on how we interact with data, stacks ensure that certain operations are highly efficient.

Key Operations and Their Time Complexity

Applications of Stacks

Stacks are widely used in programming due to their simplicity and versatility.

Common applications include:

• Expression Evaluation (e.g., infix, postfix, prefix).

• Backtracking is used to solve problems like mazes or undo operations.

• Function Call Management in programming languages.

• Parentheses Matching in strings.

• Implementing Recursion.

Implementation of Stacks

Stacks can be implemented in Python using:

• Lists: Use the `append()` and `pop()` methods.

• Collections' deque: A more efficient and optimized approach.

• Custom Classes: To add specific constraints or methods.

Example using deque:

Common Stack Variations

• Bounded Stack: A stack with a fixed size.

• Min Stack/Max Stack: Augmented stacks to retrieve the minimum or maximum element in constant time.

Stack Overflow and Underflow

• Stack Overflow occurs when pushing to a stack that exceeds its capacity.

• Stack Underflow occurs when popping from an empty stack.

Real-Life Analogies

Examples include undo/redo features, browser back buttons, and function call management.

Limitations

Stacks restrict access to only the top item and do not allow random access to arbitrary elements.

Queue and Stack Hybrid

Structures like deque combine stack and queue operations, allowing efficient access at both ends.