package com.thealgorithms.sorts;

/**
 * @author Varun Upadhyay (https://github.com/varunu28)
 * @author Podshivalov Nikita (https://github.com/nikitap492)
 * @see SortAlgorithm
 */
class BubbleSort implements SortAlgorithm {

    /**
     * Implements generic bubble sort algorithm.
     *
     * Time Complexity:
     * - Best case: O(n) – array is already sorted.
     * - Average case: O(n^2)
     * - Worst case: O(n^2)
     *
     * Space Complexity: O(1) – in-place sorting.
     *
     * @param array the array to be sorted.
     * @param <T> the type of elements in the array.
     * @return the sorted array.
     */
    @Override
    public <T extends Comparable<T>> T[] sort(T[] array) {
        for (int i = 1, size = array.length; i < size; ++i) {
            boolean swapped = false;
            for (int j = 0; j < size - i; ++j) {
                if (SortUtils.greater(array[j], array[j + 1])) {
                    SortUtils.swap(array, j, j + 1);
                    swapped = true;
                }
            }
            if (!swapped) {
                break;
            }
        }
        return array;
    }
}

Problem Statement

Given an unsorted array of n elements, write a function to sort the array

Approach

• select the first element of the array
• compare it with its next element
• if it is larger than the next element then swap them
• else do nothing
• keep doing this for every index of the array
• repeat the above process n times.

Time Complexity

O(n^2) Worst case performance

O(n) Best-case performance

O(n^2) Average performance

Space Complexity

O(1) Worst case

Founder's Name

• The term “Bubble Sort” was first used by Iverson, K in 1962.

Example

arr[] = {10, 80, 40, 30}
Indexes: 0   1   2   3    

1. Index = 0, Number = 10
2. 10 < 80, do nothing and continue

3. Index = 1, Number = 80
4. 80 > 40, swap 80 and 40
5. The array now is {10, 40, 80, 30}

6. Index = 2, Number = 80
7. 80 > 30, swap 80 and 30
8. The array now is {10, 40, 30, 80}

Repeat the Above Steps again

arr[] = {10, 40, 30, 80}
Indexes: 0   1   2   3   

1. Index = 0, Number = 10
2. 10 < 40, do nothing and continue

3. Index = 1, Number = 40
4. 40 > 30, swap 40 and 30
5. The array now is {10, 30, 40, 80}

6. Index = 2, Number = 40
7. 40 < 80, do nothing
8. The array now is {10, 30, 40, 80}

Repeat the Above Steps again

arr[] = {10, 30, 40, 80}
Indexes: 0   1   2   3   

1. Index = 0, Number = 10
2. 10 < 30, do nothing and continue

3. Index = 1, Number = 30
4. 30 < 40, do nothing and continue

5. Index = 2, Number = 40
6. 40 < 80, do nothing

Since there are no swaps in above steps, it means the array is sorted and we can stop here.

Video Explanation

A video explaining the Bubble Sort Algorithm

Others

Bubble sort is also known as Sinking sort.

Animation Explanation

• Tute Board