Stack Visualizer

Interactive visualization of the Stack data structure with push, pop, and empty operations

The Stack visualizer provides an interactive way to understand how the Stack data structure works. A Stack follows the LIFO (Last In First Out) or FILO (First In Last Out) principle, similar to a stack of books.

Try the live visualizer at dsvisualizer.isatvik.com/stack

What is a Stack?

Stack is a data structure where elements that enter last leave first. This is similar to a stack of books - you can only add or remove items from the top.

They are also known as:

• LIFO - Last In First Out
• FILO - First In Last Out

Stacks can be built using arrays or linked lists. The implementation in this visualizer uses an array-based approach.

Interactive Controls

The visualizer provides three main operations you can perform:

Push

Adds an element on top of the stack.

How to use:

1. Enter a value in the input field
2. Click the “Push” button
3. Watch the element appear at the top of the stack

Time Complexity: O(1)

Space Complexity: O(1)

Pop

Removes the top element from the stack.

How to use:

1. Click the “Pop” button
2. Watch the top element disappear from the stack

Time Complexity: O(1)

Space Complexity: O(1)

Empty

Clears all elements from the stack.

How to use:

1. Click the “Empty” button
2. Watch all elements disappear from the stack

Time Complexity: O(1)

Space Complexity: O(1)

Implementation Details

The basic structure of a Stack looks like this:

Stack.java

class stacks{
    private int[] items;
    private int count;
    private int capacity;

    // Constructor for determining the size of the stack at initialization
    public Stacks(int capacity){
        items = new int[capacity];
        this.capacity = capacity;
    }

    public void push(int value) {}
    public void pop() {}
    public int peek() {}
    public boolean isEmpty() {}
}

Key Variables

• count - Index for the next element that enters
• items - Array that holds the stack elements
• capacity - Variable that holds the length of the array

Core Operations

1. Push Operation

   The push method adds an element on top of the stack.

   push.java

   /*
    * Time: O(1)
    * Space: O(1)
    */
   public void push(int value){
       if(count == capacity) // Stack is full
           return;
       
       items[count++] = value;
   }
   

   Always check if the stack is full before pushing. The visualizer will prevent you from exceeding capacity.

2. Pop Operation

   The pop method removes the top element from the stack.

   pop.java

   /*
    * Time: O(1)
    * Space: O(1)
    */
   public int pop(){
       if(count == 0) // No elements to pop
           return;
       
       int temp = items[count - 1];
       items[count--] = 0;
       return temp;
   }
   

   Check if the stack is empty before popping to avoid errors.

3. Peek Operation

   The peek method returns the top element without removing it.

   peek.java

   /*
    * Time: O(1)
    * Space: O(1)
    */
   public int peek(){
       if(count == 0)
           return; // throw error
       
       return items[count-1];
   }
   

   The key difference: peek returns the element but doesn’t remove it, whereas pop removes the element.

4. isEmpty Operation

   Check if the stack is empty.

   isEmpty.java

   /*
    * Time: O(1)
    * Space: O(1)
    */
   public boolean isEmpty(){
       return count == 0;
   }
   

Real-World Example: Balanced Parentheses

One common application of stacks is checking for balanced brackets in expressions. The visualizer includes a bracket matching example.

1. Step 1

   Compare the first character of the string. If it’s an open bracket (, {, [, or <, push it to the stack.

   If it’s a close bracket, compare with the bracket on top of the stack using the peek method.

2. Step 2

   If the brackets aren’t corresponding pairs, the expression is not balanced.

   If they match, pop the element from the stack.

3. Step 3

   Continue until you reach the end of the string.

   If the stack is empty at the end, the parentheses are balanced.

Performance Summary

Operation	Time Complexity	Space Complexity
Push	O(1)	O(1)
Pop	O(1)	O(1)
Peek	O(1)	O(1)
isEmpty	O(1)	O(1)
Empty	O(1)	O(1)

All stack operations are extremely efficient with constant time and space complexity!