Bubble Sort

Description

Bubble Sort is a straight forward approach using brute force.
It uses 2 for loops and loops through the given array and finds the least element each time and places it in the right position during each iteration.

Algorithm

Let us consider the following array:
We assign 2 pointers, i and j. Initially, pointer i starts and stays at 0 and pointer j starts at the element next to pointer i and moves to the right until it finds an element lesser than the element at i (Ei). Our aim is to detect the smallest element to the right of Element i and place it at position i. This way the least elements are accumulated at the start of the array and hence sorting the array.
Ei = 6 Ej = 7 Ej > Ei Continue
Ei = 6 Ej = 3 Ej < Ei Swap i and j

Ei = 3 Ej = 4 Ej > Ei Continue

Ei = 3 Ej = 2 Ej < Ei Swap i and j

Ei = 2 Ej = 9 Ej > Ei Continue

Ei = 2 Ej = 0 Ej < Ei Swap i and j

Ei = 2 Ej = 9 Ej > Ei Continue

By the end of the first iteration, the element at i becomes the least number. So we increment pointer i to repeat the same process for the rest of the elements. Let’s have a look at the next iteration.
Ei = 7 Ej = 6 Ej < Ei Swap i and j

Ei = 6 Ej = 4 Ej < Ei Swap i and j

Ei = 4 Ej = 3 Ej < Ei Swap i and j

Ei = 3 Ej = 2 Ej < Ei Swap i and j

Ei = 2 Ej = 1 Ej < Ei Swap i and j

Now we have the second smaller number in the right position (index 1). Similarly repeating the process further until pointer i reaches the last but one element would give us the final sorted array.

Code

package com.softwarebook.sorting;

import lombok.extern.slf4j.Slf4j;

@Slf4j
public class BubbleSort {

    public static void main(String[] args) {
        int[] numbers = new int[] { 6, 0, 3, 4, 2, 9, 1, 7 };
        sort(numbers);
        log.info("Sorted Array: {}", numbers);
    }

    /**
     * This function swaps the elements in the given indices of a given array.
     *
     * @param numbers
     * @param a
     * @param b
     */
    public static void swap(int[] numbers, int a, int b) {
        log.info("Swapping numbers: {} and {} in array: {}", numbers[a], numbers[b], numbers);
        int temp = numbers[a];
        numbers[a] = numbers[b];
        numbers[b] = temp;
    }

    public static void sort(int[] numbers) {
        for (int i = 0; i < numbers.length; i++) {
            for (int j = i + 1; j < numbers.length; j++) {
                if (numbers[j] < numbers[i]) {
                    swap(numbers, i, j);
                }
            }
        }
    }

}