In data structure, an instance refers to a specific occurrence of a data structure. It is a concrete representation of an abstract data type. To understand what an instance is, let’s first discuss what a data structure and an abstract data type are in the context of computer science.

## Data Structure

A data structure is a way of organizing and storing data in a computer’s memory so that it can be efficiently accessed and manipulated. It provides a systematic way of organizing and managing large amounts of information to perform various operations such as searching, inserting, deleting, and sorting.

There are various types of data structures available, each designed to handle specific types of data and operations efficiently. Examples include arrays, linked lists, stacks, queues, trees, graphs, and hash tables.

## Abstract Data Type (ADT)

An abstract data type (ADT) is a high-level description of how we can manipulate the data without specifying the implementation details. It defines the behavior and properties of the data type but does not specify how these operations are implemented internally.

For example, consider the ADT “Stack”. It defines operations such as push (to insert an element), pop (to remove the top element), and peek (to view the top element), but it does not specify whether these operations are implemented using arrays or linked lists.

## Instance in Data Structure

In the context of data structures, an instance refers to a specific occurrence or instantiation of a particular ADT. It represents the actual implementation or realization of the abstract concept described by the ADT.

Let’s take an example to understand this better. Consider the ADT “Queue” which follows First-In-First-Out (FIFO) order.

An instance of this ADT could be a queue of integers: [5, 10, 15, 20]. Here, the specific occurrence of the queue with these elements represents an instance of the Queue ADT.

### Example:

To further illustrate the concept of an instance in data structures, let’s take another example using the ADT “Binary Tree”. An instance of a binary tree can be represented visually as follows:

10 / \ 5 15 / / \ 3 12 20

In this example, we have a binary tree with nodes containing integer values. This specific occurrence of a binary tree represents an instance of the Binary Tree ADT.

## Conclusion

In summary, an instance in data structure refers to a specific occurrence or instantiation of an abstract data type. It represents the concrete implementation and realization of the abstract concept described by the ADT. Instances allow us to work with and manipulate actual data structures based on their predefined properties and behaviors.