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# Which of the Following is Not a Stable Sorting Algorithm?

## What is a Sorting Algorithm?

A sorting algorithm is a set of instructions used to organize data (such as numbers or characters) into a certain order. This process is essential for many tasks, such as searching for a specific item in a database. Common sorting algorithms include insertion sort, bubble sort, and selection sort.

## What Does “Stable” Mean?

When discussing sorting algorithms, a “stable” algorithm is one that preserves the relative order of records with identical keys (that is, values). This is important when sorting items that have multiple values associated with them. For example, if you have a list of students and their grades, a stable sorting algorithm would preserve the order of students with the same grade.

## Which Algorithm Is Not Stable?

The quick sort algorithm is not considered to be stable. It is usually implemented with a divide-and-conquer approach, which works by dividing the list into smaller lists and sorting them separately. This method does not guarantee that records with equal keys will remain in the same order.

## Why Is Quick Sort Still Used?

Despite its instability, quick sort is still a popular sorting algorithm due to its efficiency. It is relatively fast and has good average-case performance, meaning it is well-suited for large datasets. Additionally, it uses a relatively small amount of memory and can be easily implemented in most programming languages.

## Conclusion

When sorting data, it is important to choose an algorithm that best fits the task. Quick sort is a popular sorting algorithm that is not considered to be stable, meaning it does not guarantee the order of records with equal keys. However, it is still widely used due to its efficiency and ease of implementation.