Bubble Sort vs Selection Sort: What is the Difference

Sorting algorithms are a fundamental concept in computer science and play an important role in many areas of computer programming.

Two of the most common sorting algorithms are bubble sort and selection sort.

In this article, we will take a deep dive into these two algorithms, discussing how they work, their time complexity, and use cases.

By the end of this article, you will have a better understanding of when to use bubble sort or selection sort and be able to confidently implement these algorithms in your own code.


Bubble Sort

Bubble sort is a simple sorting algorithm that repeatedly steps through the list to be sorted, compares each pair of adjacent items, and swaps them if they are in the wrong order.

The pass through the list is repeated until no swaps are needed, which indicates that the list is sorted.

For example, let’s say we have the following unsorted list of integers: [5, 2, 9, 1, 5].

Using bubble sort, we would first compare the first two elements (5 and 2) and swap them since 5 is larger than 2.

We would then compare the next two elements (2 and 9) and not swap them since 2 is smaller than 9.

We would then compare the next two elements (9 and 1) and swap them.

Finally, we would compare the last two elements (1 and 5) and not swap them.

This completes one pass through the list.

We would then repeat the process until no more swaps are needed, resulting in the list being sorted in ascending order: [1, 2, 5, 5, 9].

The time complexity of bubble sort is O(n^2), which means that the algorithm takes longer to sort larger lists.

This is because the algorithm needs to make n passes through the list, and on each pass, it compares and possibly swaps n-1 pairs of elements.

This is considered less efficient than other sorting algorithms and is not recommended for large lists.

However, bubble sort is a good choice for small lists or lists that are almost sorted, as it does not require much additional memory and is easy to understand and implement.

Selection Sort

Selection sort is another simple sorting algorithm that divides the input list into two parts: the sorted portion and the unsorted portion.

The algorithm repeatedly finds the minimum element from the unsorted portion and moves it to the sorted portion.

For example, let’s say we have the following unsorted list of integers: [5, 2, 9, 1, 5].

Using selection sort, we would first find the minimum element (1) in the list and swap it with the first element (5).

We would then find the next minimum element (2) and swap it with the second element (2).

This process would continue until the entire list is sorted in ascending order: [1, 2, 5, 5, 9].

Like bubble sort, the time complexity of selection sort is also O(n^2).

However, selection sort has the advantage of making only n-1 swaps, which is less than bubble sort’s n(n-1)/2 swaps.

This makes selection sort slightly more efficient than bubble sort.

Selection sort is also easy to understand and implement and is a good choice for small lists or lists that are almost sorted.

Comparison between Bubble Sort and Selection Sort

When comparing bubble sort and selection sort, the main difference is the number of swaps made.

Bubble sort makes n(n-1)/2 swaps while selection sort makes n-1 swaps.

This makes selection sort slightly more efficient than bubble sort.

However, both algorithms have the same time complexity of O(n^2) and are not recommended for large lists.

In terms of use cases, both bubble sort and selection sort are good choices for small lists or lists that are almost sorted.

They are also easy to understand and implement, making them a good choice for beginners learning about sorting algorithms.

However, for larger lists or lists with a high degree of disorder, more efficient algorithms such as quicksort or merge sort should be used.

To summarize the comparison, here is a table that highlights the main differences between bubble sort and selection sort:

AlgorithmTime ComplexitySwapsGood for small lists or almost sorted listsEfficient for large lists
Bubble Sort
O(n^2)
n(n-1)/2YesNo
Selection Sort
O(n^2)
n-1YesNo

Conclusion

In this blog post, we have explored bubble sort and selection sort, two common sorting algorithms.

We have discussed how they work, their time complexity, and use cases.

We have also compared the two algorithms and highlighted their main differences. While bubble sort and selection sort are not the most efficient algorithms for large lists, they are good choices for small lists or lists that are almost sorted.

We encourage you to try implementing these algorithms on your own to gain a deeper understanding of how they work.

For further learning on sorting algorithms, we recommend checking out resources such as “Introduction to Algorithms” by Cormen et al. and “Algorithms in C” by Robert Sedgewick.