Stacks

In the world of data structures, a stack is a linear data structure that follows the Last In, First Out (LIFO) principle. It can be visualized as a stack of books, where the topmost book is the most recently added and the bottom book is the least recently added.

Applications of Stacks

Stacks have various applications in computer science and are commonly used in algorithms and programming. Some examples include:

1. Function Call Stack: Stacks are used to manage function calls in languages like Java. When a function is called, its local variables and parameters are pushed onto the stack, and when the function returns, they are popped off the stack.

2. Expression Evaluation: Stacks are used to evaluate arithmetic expressions, check for balanced parentheses, and convert infix expressions to postfix (or prefix) notation for algorithmic evaluation.

3. Undo/Redo Operations: Stacks can be used to implement undo and redo functionality in text editors or graphical user interfaces. Each action or operation is pushed onto the stack, allowing users to reverse or redo changes.

Java Example

Let's take a look at an example of creating, modifying, and accessing elements in a stack using Java:

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import java.util.Stack;

​

public class Main {

  public static void main(String[] args) {

    // Create a stack

    Stack<String> stack = new Stack<>();

​

    // Push elements onto the stack

    stack.push("Alice");

    stack.push("Bob");

    stack.push("Charlie");

​

    // Print the stack

    System.out.println(stack);

​

    // Peek at the top element

    String topElement = stack.peek();

    System.out.println("Top element: " + topElement);

​

    // Pop an element from the stack

    String poppedElement = stack.pop();

​

    // Print the popped element

    System.out.println("Popped element: " + poppedElement);

​

    // Print the updated stack

    System.out.println(stack);

  }

}