Bubble Sort: A Simple But Inefficient Sorting Algorithm
Bubble sort is one of the simplest sorting algorithms that works by repeatedly swapping the adjacent elements if they are in the wrong order. It is easy to understand and implement, but it is very slow and inefficient for large data sets. In this article, we will learn about the bubble sort algorithm, its complexity analysis, its advantages and disadvantages, its applications, its optimization, and its comparison with other sorting algorithms.
bubble sort
What is Bubble Sort?
Bubble sort is a sorting algorithm that compares two adjacent elements and swaps them until they are in the intended order. Just like the movement of air bubbles in the water that rise up to the surface, each element of the array moves to the end in each iteration. Therefore, it is called a bubble sort. It is also referred to as comparison or sinking sort.
How does Bubble Sort work?
Suppose we are trying to sort the elements in ascending order. The algorithm works as follows:
Starting from the first index, compare the first and the second elements. If the first element is greater than the second element, they are swapped.
Now, compare the second and the third elements. Swap them if they are not in order.
The above process goes on until the last element.
After each iteration, the largest element among the unsorted elements is placed at the end.
In each iteration, the comparison takes place up to the last unsorted element.
The array is sorted when all the unsorted elements are placed at their correct positions.
Here is an example of bubble sort visualized:
The above image shows how bubble sort works on an array of 6 elements. The red bars indicate the elements that are being compared and swapped. The green bars indicate the elements that are already sorted. The number of iterations is equal to the number of elements minus one.
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Pseudocode of Bubble Sort
Here is a pseudocode of bubble sort algorithm:
procedure bubbleSort(A : list of sortable items) n := length(A) for i := 0 to n-1 inclusive do for j := 0 to n-i-1 inclusive do //the elements aren't in the right order if A[j] > A[j+1] then //swap the elements swap(A[j], A[j+1]) end if end for end for end procedure
Complexity Analysis of Bubble Sort
In this section, we will analyze the time and space complexity of bubble sort algorithm.
Time Complexity
The time complexity of an algorithm is a measure of how much time it takes to run based on the input size. The time complexity of bubble sort depends on how many comparisons and swaps it performs in each iteration.
The worst-case time complexity of bubble sort is O(N), where N is the number of elements in the array. This happens when the array is in reverse order and every element needs to be swapped in every iteration.
The best-case time complexity of bubble sort is O(N), where N is the number of elements in the array. This happens when the array is already sorted and no swaps are needed in any iteration.
The average-case time complexity of bubble sort is also O(N), where N is the number of elements in the array. This happens when the array is partially sorted and some swaps are needed in some iterations.
Here is a table that summarizes the time complexity of bubble sort:
Case
Time Complexity
Worst
O(N)
Best
O(N)
Average
O(N)
Space Complexity
The space complexity of an algorithm is a measure of how much extra space it requires to run based on the input size. The space complexity of bubble sort is O(1), which means it requires a constant amount of extra space regardless of the input size. This is because bubble sort only uses one temporary variable to swap the elements and does not require any additional data structures.
Advantages and Disadvantages of Bubble Sort
In this section, we will discuss the pros and cons of bubble sort algorithm.
Advantages
Bubble sort is easy to understand and implement. It does not require any complex logic or data structures.
Bubble sort is stable, which means it preserves the relative order of equal elements in the array. This is important for some applications that rely on the original order of the data.
Bubble sort can detect if the array is already sorted in the first iteration and stop the sorting process. This makes it efficient for nearly sorted arrays.
Bubble sort does not require much extra space. It only uses one temporary variable to swap the elements.
Disadvantages
Bubble sort is very slow and inefficient for large data sets. It has a quadratic time complexity, which means it takes much longer to sort as the input size increases.
Bubble sort performs many unnecessary comparisons and swaps even if the array is partially sorted. It does not adapt to the existing order of the data.
Bubble sort is not suitable for parallel or distributed computing. It cannot take advantage of multiple processors or machines to speed up the sorting process.
Bubble sort is not widely used in real-world applications. There are many other sorting algorithms that are faster and more efficient than bubble sort.
Applications of Bubble Sort
Despite its drawbacks, bubble sort can be useful for some specific applications. Here are some examples:
Bubble sort can be used to teach the basic concepts of sorting algorithms to beginners. It helps them understand how comparison and swapping work and how to analyze the complexity of an algorithm.
Bubble sort can be used to sort small data sets that are already nearly sorted. It can perform well in such cases as it can detect the sorted order in the first iteration and stop the sorting process.
Bubble sort can be used to sort data that is stored in a linked list or an array with limited memory. It does not require any extra space or data structures to perform the sorting.
Bubble sort can be used to implement other sorting algorithms such as cocktail shaker sort, comb sort, or gnome sort. These algorithms are variations of bubble sort that improve its performance by modifying some aspects of its logic.
Optimization of Bubble Sort
In this section, we will learn how to optimize bubble sort algorithm to improve its performance.
How to optimize Bubble Sort?
One way to optimize bubble sort is to keep track of the last swapped position in each iteration. This position indicates the boundary of the unsorted elements in the array. Therefore, we do not need to compare or swap any elements beyond this position in the next iteration. This reduces the number of comparisons and swaps and improves the time complexity of bubble sort.
Pseudocode of Optimized Bubble Sort
Here is a pseudocode of optimized bubble sort algorithm:
procedure optimizedBubbleSort(A : list of sortable items) n := length(A) //initialize the boundary as n-1 boundary := n-1 //repeat until no swaps are made repeat //initialize a flag to indicate if any swap is made swapped := false //initialize a new boundary as 0 newBoundary := 0 for i := 0 to boundary-1 inclusive do //the elements aren't in the right order if A[i] > A[i+1] then //swap the elements swap(A[i], A[i+1]) //set the flag to true //update the new boundary as i newBoundary := i end if end for //update the boundary as the new boundary boundary := newBoundary until not swapped end procedure
Comparison with other Sorting Algorithms
In this section, we will compare bubble sort with some other common sorting algorithms such as selection sort, insertion sort, merge sort, and quick sort. We will compare them based on their time complexity, space complexity, stability, and adaptability.
Algorithm
Time Complexity
Space Complexity
Stability
Adaptability
Bubble Sort
O(N)
O(1)
Yes
No
Selection Sort
O(N)
O(1)
No
No
Insertion Sort
O(N)
O(1)
Yes
Yes
Merge Sort
O(N log N)
O(N)
Yes
No
Quick Sort
O(N log N)
O(log N)
No
No
As we can see from the table, bubble sort is not very efficient compared to other sorting algorithms. It has the same quadratic time complexity as selection sort and insertion sort, but it is less stable and less adaptable. It is also much slower than merge sort and quick sort, which have logarithmic time complexity, but it requires less space. Therefore, bubble sort is only suitable for small and nearly sorted data sets.
Conclusion
Bubble sort is a simple but inefficient sorting algorithm that works by repeatedly swapping the adjacent elements if they are in the wrong order. It has a quadratic time complexity, a constant space complexity, and a stable behavior. It can be optimized by keeping track of the last swapped position in each iteration. It can be useful for some specific applications such as teaching, sorting small and nearly sorted data sets, sorting data in a linked list or an array with limited memory, and implementing other sorting algorithms. However, it is not widely used in real-world applications as there are many other sorting algorithms that are faster and more efficient than bubble sort.
FAQs
Here are some frequently asked questions about bubble sort:
Why is bubble sort called bubble sort?
Bubble sort is called bubble sort because it resembles the movement of air bubbles in the water that rise up to the surface. Each element of the array moves to the end in each iteration like a bubble.
Is bubble sort a good algorithm?
Bubble sort is not a good algorithm for large data sets as it is very slow and inefficient. It performs many unnecessary comparisons and swaps even if the array is partially sorted. It does not adapt to the existing order of the data. It is also not suitable for parallel or distributed computing. However, it can be good for some specific applications such as teaching, sorting small and nearly sorted data sets, sorting data in a linked list or an array with limited memory, and implementing other sorting algorithms.
How can we improve bubble sort?
We can improve bubble sort by optimizing it to reduce the number of comparisons and swaps. One way to optimize bubble sort is to keep track of the last swapped position in each iteration. This position indicates the boundary of the unsorted elements in the array. Therefore, we do not need to compare or swap any elements beyond this position in the next iteration.
What are some variations of bubble sort?
Some variations of bubble sort are cocktail shaker sort, comb sort, and gnome sort. These algorithms are based on bubble sort but modify some aspects of its logic to improve its performance.
What are some alternatives to bubble sort?
Some alternatives to bubble sort are selection sort, insertion sort, merge sort, and quick sort. These algorithms are faster and more efficient than bubble sort for large data sets. They have different time and space complexities, stability, and adaptability.
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