# What Is Double Stack in Data Structure?

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Larry Thompson

The concept of a double stack in data structure is an important one to understand. In this tutorial, we will dive into what a double stack is, how it works, and its applications. Let’s get started!

## What is a Double Stack?

A double stack, also known as a dual stack or two-stack, is a type of data structure that allows for the storage and retrieval of elements from both ends. Unlike a regular stack, which follows the Last-In-First-Out (LIFO) principle, a double stack allows elements to be inserted and removed from both the top and bottom simultaneously.

Double stacks have two pointers, one pointing to the top of the first stack (Stack 1) and another pointing to the top of the second stack (Stack 2). These stacks can either grow towards each other or away from each other based on implementation.

## How Does it Work?

The working principle of a double stack is quite simple. You can push elements onto either Stack 1 or Stack 2, and you can pop elements from either Stack 1 or Stack 2. This gives you more flexibility in terms of how you manage your data.

When inserting an element into Stack 1, you increment the pointer for Stack 1 by one and insert the element at that position. Similarly, when inserting an element into Stack 2, you decrement the pointer for Stack 2 by one and insert the element at that position.

To remove an element from Stack 1, you simply decrement the pointer for Stack 1 by one and retrieve the element at that position. Likewise, to remove an element from Stack 2, you increment the pointer for Stack 2 by one and retrieve the element at that position.

### Example:

Consider the following example of a double stack:

``` Stack 1: [5, 4, 3] Stack 2: [8, 9, 2] ```

If we push the element 7 onto Stack 1 and push the element 6 onto Stack 2, our double stack would look like this:

``` Stack 1: [5, 4, 3, 7] Stack 2: [8, 9, 6, 2] ```

If we pop an element from Stack 1 and Stack 2 simultaneously, we would get the elements 7 and 6, respectively. Our double stack would then look like this:

``` Stack 1: [5, 4, 3] Stack 2: [8, 9, 6, 2] ```

## Applications of Double Stacks

The double stack data structure has various applications in computer science and software development. Some common applications include:

• Evaluation of arithmetic expressions: Double stacks can be used to evaluate arithmetic expressions by storing operands in one stack and operators in another.
• Infix to postfix conversion: Double stacks are useful in converting infix expressions to postfix expressions.
• Maintaining two different sets of data: Double stacks can be used to maintain two separate sets of data simultaneously.
• Solving complex problems: Double stacks can be employed in solving complex problems that require handling data from both ends.

Overall, the double stack data structure is a versatile and powerful tool in computer science. By allowing elements to be inserted and removed from both ends, it provides enhanced flexibility and opens up new possibilities for solving various problems.

Now that you have a clear understanding of what a double stack is and how it works, you can explore its applications further and apply it to your own projects. Happy coding!