# What Data Structure Does Vector Use?

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Larry Thompson

Data structures are an essential part of programming, as they allow us to store and organize data efficiently. One commonly used data structure in many programming languages, including C++, is the vector. But what kind of data structure does a vector use?

## Introduction to Vectors

A vector is a dynamic array that can grow or shrink in size. It is a container that allows us to store and manipulate elements in a sequential manner. Vectors are widely used because they provide the benefits of both arrays and linked lists, making them an excellent choice for many applications.

## Underlying Data Structure

The underlying data structure used by vectors is typically an array. When we create a vector, it allocates a block of contiguous memory to hold its elements. This means that the elements of a vector are stored in adjacent memory locations.

Why use an array?

Arrays provide constant time access to individual elements based on their position or index. This allows vectors to access and modify elements at any position efficiently using random access.

## Expanding and Shrinking the Vector

Vectors have the unique ability to expand and shrink dynamically based on the number of elements they hold. When we add elements beyond the capacity of the current allocated memory, vectors automatically allocate more memory by creating a new larger array and copying existing elements into it.

• Expanding: When expanding, vectors typically double their current capacity to ensure efficient growth without frequent reallocations. This amortized doubling strategy reduces the number of reallocations required as more elements are added.
• Shrinking: On the other hand, when we remove elements from a vector, it may not immediately release the allocated memory back to the system. Vectors often keep some extra capacity to accommodate future growth, avoiding frequent reallocations in case of subsequent insertions.

## Vector vs. Linked List

Vectors and linked lists are both dynamic data structures, but they differ in terms of their underlying implementation and use cases.

Arrays: Vectors, backed by arrays, provide efficient random access to elements but have slower insertions and deletions in the middle due to shifting elements.

Linked Lists: Linked lists, on the other hand, use nodes connected through pointers. They allow fast insertions and deletions in the middle but have slower random access as we need to traverse from the start or end of the list.

### Conclusion

In summary, vectors use arrays as their underlying data structure to provide efficient random access to elements. They can dynamically expand and shrink their size based on the number of elements they hold. Vectors strike a balance between array-like constant time access and linked list-like dynamic resizing, making them a versatile choice for many programming scenarios.

So next time you work with vectors in C++ or any other language that supports them, you’ll know what data structure is at play behind the scenes!