Data Structures: Stacks Overview

Data Structures

• A stack is a linear data structure that follows the Last-In, First-Out (LIFO) principle.
• Elements are added (pushed) and removed (popped) from the top of the stack.
• Stacks are commonly used in algorithms and data processing, offering a way to manage and retrieve data sequentially.

Operations

• Push: Adds an element to the top of the stack.
• Pop: Removes and returns the element at the top of the stack.
• Peek or Top: Returns the element at the top of the stack without removing it.
• IsEmpty: Checks if the stack is empty.
• IsFull: Checks if the stack is full (relevant for stacks with a fixed size).

Implementations

• Arrays: A simple and efficient way to implement a stack using a fixed-size array.
• Linked Lists: A flexible alternative, where the stack's size is not predetermined.

Applications

• Function calls (call stack): The call stack manages the order in which functions are executed during runtime, ensuring correct function returns.
• Undo/Redo operations: A stack helps to manage redo/undo actions by keeping a record of previous states.
• Expression evaluation (infix to postfix): Stacks are useful in converting infix expressions to postfix notation for evaluation.
• Depth-first search (DFS) graph traversal: The stack stores nodes during graph traversal.
• Balancing symbols (parentheses, brackets, braces): A stack can efficiently check for matching pairs.
• Backtracking algorithms: To manage possible solutions during backtracking.

Advantages

• Simplicity: Relatively straightforward implementation.
• Efficiency: Basic stack operations are typically fast (O(1)).
• Versatility: Useful in various algorithmic problems.

Disadvantages

• Limited capacity (fixed-size arrays): Can cause issues if more elements need to be added than anticipated.
• Space consumption (linked lists): Linked list implementation requires more memory overhead than arrays.

Example Scenarios

• Function calls: When a function funcB calls a function funcA, funcB is placed onto the stack, and funcA is called. Once funcA finishes, funcB is popped, and execution continues where it left off.
• Expression Evaluation: Consider the expression "2 + 3 * 4". Parsing the expression, operator precedence is applied using the stack.