Question 77 : Write an algorithm to implement bubble sort?

 Bubble sort algorithm

Bubble sort works by iterating the first element to the last element, comparing two adjacent elements, and swapping them if they are not in the correct order. Each iteration places the next larger value in its correct place.

Why bubble sort is called bubble sort or sinking sort(From Wikipedia)

Bubble sort can be done in ascending order or descending order.

Reason for being called Sinking sort

The larger values might be regarded as heavier and therefore be seen to progressively sink to the bottom of the list.

Reason for being called Bubble sort

The smaller values might be regarded as lighter and therefore be seen to progressively bubble up to the top of the list

Bubble sort Implementation

I have printed intermediate steps to understand it better:

public class BubbleSortMain {

 public static void main(String args[])
 {
  int  arr[]={100,20,15,30,5,75,40};
  bubbleSort(arr);
 
 }
 
 public static int[] bubbleSort(int arr[])
 {
  for (int i = 0; i < arr.length; i++) {
   for (int j = 0; j < arr.length-1-i; j++) { 
     if(arr[j]>arr[j+1])
     {
       int temp=arr[j];
       arr[j]=arr[j+1];
       arr[j+1]=temp;
     }
   }
   System.out.print("Iteration "+(i+1)+": ");
   printArray(arr);
  }
  return arr;
 }
 
 public static void printArray(int arr[])
 {
  for (int i = 0; i <arr.length; i++) {
   System.out.print(arr[i]+" ");
  }
  System.out.println();
 }
}

When you run above program, you will get following output:

Iteration 1: 20 15 30 5 75 40 100
Iteration 2: 15 20 5 30 40 75 100
Iteration 3: 15 5 20 30 40 75 100
Iteration 4: 5 15 20 30 40 75 100
Iteration 5: 5 15 20 30 40 75 100
Iteration 6: 5 15 20 30 40 75 100
Iteration 7: 5 15 20 30 40 75 100

You may notice that each iteration places the next larger element in its correct place.

Time Complexity:

Best case: O(n)

Average case: O(n^2)

Worst case: O(n^2)

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