# Bubble Sort vs. Selection Sort — What's the Difference?

By Tayyaba Rehman — Published on December 5, 2023
Bubble Sort repeatedly swaps adjacent elements if out of order, while Selection Sort finds the smallest (or largest) element and places it in its final position.

## Key Differences

Bubble Sort operates by comparing adjacent elements in a list and swapping them if they're out of order, ensuring the largest (or smallest) element bubbles up to its correct position after each pass. In contrast, Selection Sort divides the input into a sorted and an unsorted region, continually selecting the smallest (or largest) element from the unsorted region and placing it in the sorted one.
In terms of efficiency, both Bubble Sort and Selection Sort have an average and worst-case time complexity of O(n^2), where n is the number of elements. However, Bubble Sort generally makes more swaps and comparisons than Selection Sort for the same input.
Bubble Sort is often regarded as one of the most straightforward sorting algorithms to understand and implement. On the flip side, Selection Sort is also conceptually simple, focusing on selecting the smallest (or largest) element repeatedly.
The primary advantage of Bubble Sort is that it can determine if a list is already sorted in a single pass, making its best-case time complexity O(n). Conversely, Selection Sort does not have this adaptive property and always performs the same number of comparisons, regardless of the input order.
A key characteristic of Bubble Sort is its adaptability; if during a pass no swaps are made, it knows the list is sorted and can break early. On the other hand, Selection Sort does not have this capability, consistently going through all its iterations even if the list is partially or entirely sorted.

## Comparison Chart

### Method

Swaps adjacent elements if out of order
Finds smallest (or largest) and places in final position

### Efficiency

Generally more swaps than Selection Sort
Typically fewer swaps than Bubble Sort

### Concept

"Bubbling" the largest element to its correct position
Continually "selecting" the smallest element

### Best-case Time Complexity

O(n) (if list is already sorted)
O(n^2) always

Can determine if list is sorted and break early
Always performs full number of comparisons

## Compare with Definitions

#### Bubble Sort

Has a best-case time complexity of O(n) if the list is already sorted.
The benefit of Bubble Sort is its efficiency on nearly sorted data.

#### Selection Sort

Divides the list into sorted and unsorted regions.
Using Selection Sort, he saw the sorted part of the list grow with each iteration.

#### Bubble Sort

Known for its method of "bubbling" the largest element up.
Using Bubble Sort, the largest number ended up at the end of the list after the first pass.

#### Selection Sort

A sorting algorithm that selects the smallest (or largest) element and places it in its sorted position.
He was intrigued by the method Selection Sort used to pick the smallest number repeatedly.

#### Bubble Sort

A sorting algorithm that swaps adjacent elements if out of order.
She learned Bubble Sort as her first sorting technique in the class.

#### Selection Sort

Typically makes fewer swaps than Bubble Sort.
He preferred Selection Sort over Bubble Sort when minimizing swaps was crucial.

#### Bubble Sort

Recognizable by its repetitive adjacent element comparisons.
While applying Bubble Sort, he noticed many adjacent swaps in the list.

#### Selection Sort

Known for its consistent number of comparisons, irrespective of input.
Unlike some other algorithms, Selection Sort took the same time on both sorted and unsorted lists.

#### Bubble Sort

Often taught to beginners due to its simplicity.
In introductory computer science, Bubble Sort was the first algorithm she coded.

#### Selection Sort

Continually selects the smallest element until the list is sorted.
With each pass of Selection Sort, the next smallest number found its place.

## Common Curiosities

#### Which sorting algorithm is often taught first to beginners?

Bubble Sort is often introduced first due to its simplicity.

#### What's the primary method of Bubble Sort?

Bubble Sort swaps adjacent elements if they're out of order.

#### Which sort typically performs more swaps, Bubble or Selection?

Bubble Sort generally makes more swaps than Selection Sort.

#### Is Bubble Sort efficient on nearly sorted data?

Yes, Bubble Sort's best-case time complexity is O(n) if the list is already sorted.

#### Can Bubble Sort detect when the list becomes sorted?

Yes, if no swaps are made during a pass, Bubble Sort knows the list is sorted and can break early.

#### Why is Bubble Sort called "Bubble" Sort?

It's named for the way the largest element "bubbles up" to its correct position during each pass.

#### Does Selection Sort have an adaptive nature like Bubble Sort?

No, Selection Sort always performs its full number of comparisons, even on sorted data.

#### How many passes does Selection Sort require?

Selection Sort requires n-1 passes for a list of n elements.

#### How does Selection Sort work?

Selection Sort selects the smallest (or largest) element and places it in its final sorted position.

#### How does Selection Sort handle already sorted lists?

Selection Sort performs the same number of comparisons, regardless of whether the list is sorted or not.

#### Are there any situations where Selection Sort is preferable?

Selection Sort might be preferable when minimizing the number of swaps is more crucial than comparisons.

#### How do the time complexities of Bubble and Selection Sort compare?

Both have an average and worst-case time complexity of O(n^2), but Bubble Sort can be O(n) in the best case.

#### Which algorithm is more intuitive for beginners?

Both are relatively straightforward, but many find Bubble Sort's "bubbling" method slightly more intuitive.

#### Are these sorts used in real-world applications?

They're primarily educational due to their inefficiencies, but they might be used in specific contexts on small datasets.

#### How does Selection Sort decide which element to swap?

It consistently selects the smallest (or largest) element from the unsorted region and swaps it with the first unsorted element.