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Bubble sort, also referred to as comparison sort, is a simple sorting algorithm that repeatedly goes through the list, compares adjacent elements and swaps them if they are in the wrong order. This is the most simplest algorithm and inefficient at the same time. Yet, it is very much necessary to learn about it as it represents the basic foundations of sorting.
Table of Content
O(n)
.Algorithm: We compare adjacent elements and see if their order is wrong (i.e a[i] > a[j] for 1 <= i < j <= size of array
; if array is to be in ascending order, and vice-versa). If yes, then swap them.
Explanation:
n
. To sort this array we do the above step (swapping) for n - 1
passes.ith
pass, at least one element from (n - i + 1)
elements from start will go at its right place. That element will be the ith (for 1 <= i <= n - 1)
largest element of the array. Because in the ith
pass of the array, in the jth
iteration (for 1 <= j <= n - i)
, we are checking if a[j] > a[j + 1]
, and a[j]
will always be greater than a[j + 1]
when it is the largest element in range [1, n - i + 1]
. Now we will swap it. This will continue until ith
largest element is at the (n - i + 1)
th position of the array.Consider the following array: Arr=14, 33, 27, 35, 10
. We need to sort this array using bubble sort algorithm.
First Pass:
We proceed with the first and second element i.e., Arr[0] and Arr[1]. Check if 14 > 33
which is false. So, no swapping happens and the array remains the same.
We proceed with the second and third element i.e., Arr[1] and Arr[2]. Check if 33 > 27
which is true. So, we swap Arr[1] and Arr[2].
Thus the array becomes:
We proceed with the third and fourth element i.e., Arr[2] and Arr[3]. Check if 33 > 35
which is false. So, no swapping happens and the array remains the same.
We proceed with the fourth and fifth element i.e., Arr[3] and Arr[4]. Check if 35 > 10
which is true. So, we swap Arr[3] and Arr[4].
Thus, after swapping the array becomes:
Thus, marks the end of the first pass, where the Largest element reaches its final(last) position.
Second Pass:
We proceed with the first and second element i.e., Arr[0] and Arr[1]. Check if 14 > 27
which is false. So, no swapping happens and the array remains the same.
We now proceed with the second and third element i.e., Arr[1] and Arr[2]. Check if 27 > 33 which is false. So, no swapping happens and the array remains the same.
We now proceed with the third and fourth element i.e., Arr[2] and Arr[3]. Check if 33 > 10
which is true. So, we swap Arr[2] and Arr[3].
Now, the array becomes
Thus marks the end of second pass where the second largest element in the array has occupied its correct position.
Third Pass:
After the third pass, the third largest element will be at the third last position in the array.
.
.
i-th Pass:
After the ith pass, the ith largest element will be at the ith last position in the array.
.
.
n-th Pass:
After the nth pass, the nth largest element(smallest element) will be at nth last position(1st position) in the array, where ‘n’ is the size of the array.
After doing all the passes, we can easily see the array will be sorted.
Thus, the sorted array will look like this:
bubbleSort( Arr[], totat_elements) for i = 0 to total_elements - 1 do: swapped = false for j = 0 to total_elements - i - 2 do: /* compare the adjacent elements */ if Arr[j] > Arr[j+1] then /* swap them */ swap(Arr[j], Arr[j+1]) swapped = true end if end for /*if no number was swapped that means array is sorted now, break the loop.*/ if(not swapped) then break end if end for end
Implementation of bubble sort in C
#include<stdio.h>
int main()
{
int arr[] = {5, 6, 2 ,6, 9, 0, -1}, n = 7, i, j;
for(i = 0; i < n - 1; ++i)
{
int swapped = 0;
for(j = 0; j < (n - i - 1); ++j)
if(arr[j] > arr[j+1])
{
int temp = arr[j];
arr[j] = arr[j+1];
arr[j+1] = temp;
swapped = 1;
}
if(!swapped)
break;
}
printf("\nArray after sorting: ");
for(i = 0; i < n; ++i)
printf("%d ", arr[i]);
return 0;
}
Implementation of Bubble sort in C++
#include <iostream>
#include <vector>
using namespace std;
void BubbleSort (vector<int> &arr, int n)
{
for (int i = 0; i < n - 1; ++i)
{
bool swapped = false;
for (int j = 0; j < n - i - 1; ++j)
{
if (arr[j] > arr[j+1]) //check if adjacent element is
//not in order
{
swap(arr[j], arr[j + 1]);
swapped = true;
}
}
// Value at n-i-1 will be maximum of all the values below this index.
if(!swapped)
break;
}
}
int main()
{
vector<int> arr = {5, 6, 2, 6, 9, 0, -1};
int n = 7;
BubbleSort(arr, n);
// Display the sorted data.
cout << "\nSorted Data: ";
for (i = 0; i < n; i++)
Cout << arr[i] << “ “;
return 0;
}
Implementation of Bubble Sort in Java:
import java.util.Scanner;
class BubbleSort {
public static void main(String []args) {
int n;
Scanner in = new Scanner(System.in);
System.out.println("Input number of integers to sort");
n = in.nextInt();
int array[] = new int[n];
System.out.println("Enter " + n + " integers");
for (int i = 0; i < n; i++)
array[i] = in.nextInt();
for (int i = 0; i < n - 1; i++) {
Boolean swapped = false;
for (int j = 0; j < n - i - 1; j++) {
if (array[j] > array[j+1]) /* For descending order use < */
{
int temp = array[j];
array[j]= array[j+1];
array[j+1] = temp;
swapped = true;
}
}
if(!swapped)
break;
}
System.out.println("Sorted list of numbers:");
for (int i = 0; i < n; i++)
System.out.println(array[i]);
}
}
Implementation of bubble sort in python
def bubble_sort(arr):
for i in range(len(arr) - 1):
swapped = False
for j in range(0, len(arr) - i - 1):
if arr[j] > arr[j + 1]:
arr[j], arr[j + 1] = arr[j + 1], arr[j]
swapped = True
if not swapped:
return
arr = [int(x) for x in input(‘Enter numbers: ’).split()]
bubble_sort(arr)
print('Sorted list: ', end='')
print(arr)
swapped
variable will be false). So, when this happens, we break from the loop after the very first iteration. Hence, time complexity in the best case scenario is O(n)
because it has to traverse through all the elements once.n-1
comparisons are done in the 1st pass, n-2
in 2nd pass, n-3
in 3rd pass and so on. So, the total number of comparisons will be:
Sum = (n-1) + (n-2) + (n-3) + ..... + 3 + 2 + 1
Sum = n(n-1)/2
Hence, the time complexity is of the order n^{2} or O(n^{2}).The space complexity for the algorithm is O(1), because only a single additional memory space is required i.e. for temporary variable used for swapping.
What is the best case time complexity of bubble sort?
The time complexity in the best case scenario is O(n)
because it has to traverse through all the elements once to recognize that the array is already sorted.
What is the advantage of bubble sort over other sorting techniques?
O(n)
.Why bubble sort is called “bubble” sort?
The “bubble” sort is called so because the list elements with greater value than their surrounding elements “bubble” towards the end of the list. For example, after first pass, the largest element is bubbled towards the right most position. After second pass, the second largest element is bubbled towards the second last position in the list and so on.
Is bubble sort a stable algorithm?
Is bubble sort an inplace algorithm?
Is Bubble sort slow?
Can bubble sort be implemented recursively?
recursiveBubbleSort(arr[], n){
// Base case
if (n == 1)
return;
// One pass of bubble sort. After
// this pass, the largest element
// is moved (or bubbled) to end.
for(i=0; i<n-1; i++){
if(arr[i] > arr[i+1])
{
swap(arr[i], arr[i+1]);
}
}
// recursion for remaining elements in array
recursiveBubbleSort(arr, n-1);
}
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