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Bubble Sort

  • Difficulty Level : Easy
  • Last Updated : 11 May, 2022
 

Bubble Sort is the simplest sorting algorithm that works by repeatedly swapping the adjacent elements if they are in the wrong order. This algorithm is not suitable for large data sets as its average and worst case time complexity is quite high.

How Bubble Sort Works?

Consider an array arr[] = {5, 1, 4, 2, 8}

First Pass: 

  • Bubble sort starts with very first two elements, comparing them to check which one is greater.
    • ( 5 1 4 2 8 ) –> ( 1 5 4 2 8 ), Here, algorithm compares the first two elements, and swaps since 5 > 1. 
    • ( 1 5 4 2 8 ) –>  ( 1 4 5 2 8 ), Swap since 5 > 4 
    • ( 1 4 5 2 8 ) –>  ( 1 4 2 5 8 ), Swap since 5 > 2 
    • ( 1 4 2 5 8 ) –> ( 1 4 2 5 8 ), Now, since these elements are already in order (8 > 5), algorithm does not swap them.

Second Pass: 

  • Now, during second iteration it should look like this:
    • ( 1 4 2 5 8 ) –> ( 1 4 2 5 8 ) 
    • ( 1 4 2 5 8 ) –> ( 1 2 4 5 8 ), Swap since 4 > 2 
    • ( 1 2 4 5 8 ) –> ( 1 2 4 5 8 ) 
    • ( 1 2 4 5 8 ) –>  ( 1 2 4 5 8

Third Pass: 

  • Now, the array is already sorted, but our algorithm does not know if it is completed.
  • The algorithm needs one whole pass without any swap to know it is sorted.
    • ( 1 2 4 5 8 ) –> ( 1 2 4 5 8 ) 
    • ( 1 2 4 5 8 ) –> ( 1 2 4 5 8 ) 
    • ( 1 2 4 5 8 ) –> ( 1 2 4 5 8 ) 
    • ( 1 2 4 5 8 ) –> ( 1 2 4 5 8

Illustration:

bubble-sort

 

Following are the implementations of Bubble Sort. 

C++




// C++ program for implementation
// of Bubble sort
#include <bits/stdc++.h>
using namespace std;
 
// A function to implement bubble sort
void bubbleSort(int arr[], int n)
{
    int i, j;
    for (i = 0; i < n - 1; i++)
 
        // Last i elements are already
        // in place
        for (j = 0; j < n - i - 1; j++)
            if (arr[j] > arr[j + 1])
                swap(arr[j], arr[j + 1]);
}
 
// Function to print an array
void printArray(int arr[], int size)
{
    int i;
    for (i = 0; i < size; i++)
        cout << arr[i] << " ";
    cout << endl;
}
 
// Driver code
int main()
{
    int arr[] = { 5, 1, 4, 2, 8};
    int N = sizeof(arr) / sizeof(arr[0]);
    bubbleSort(arr, N);
    cout << "Sorted array: \n";
    printArray(arr, N);
    return 0;
}
// This code is contributed by rathbhupendra

C




// C program for implementation of Bubble sort
#include <stdio.h>
 
void swap(int* xp, int* yp)
{
    int temp = *xp;
    *xp = *yp;
    *yp = temp;
}
 
// A function to implement bubble sort
void bubbleSort(int arr[], int n)
{
    int i, j;
    for (i = 0; i < n - 1; i++)
 
        // Last i elements are already in place
        for (j = 0; j < n - i - 1; j++)
            if (arr[j] > arr[j + 1])
                swap(&arr[j], &arr[j + 1]);
}
 
/* Function to print an array */
void printArray(int arr[], int size)
{
    int i;
    for (i = 0; i < size; i++)
        printf("%d ", arr[i]);
    printf("\n");
}
 
// Driver program to test above functions
int main()
{
    int arr[] = { 64, 34, 25, 12, 22, 11, 90 };
    int n = sizeof(arr) / sizeof(arr[0]);
    bubbleSort(arr, n);
    printf("Sorted array: \n");
    printArray(arr, n);
    return 0;
}

Java




// Java program for implementation of Bubble Sort
class BubbleSort {
    void bubbleSort(int arr[])
    {
        int n = arr.length;
        for (int i = 0; i < n - 1; i++)
            for (int j = 0; j < n - i - 1; j++)
                if (arr[j] > arr[j + 1]) {
                    // swap arr[j+1] and arr[j]
                    int temp = arr[j];
                    arr[j] = arr[j + 1];
                    arr[j + 1] = temp;
                }
    }
 
    /* Prints the array */
    void printArray(int arr[])
    {
        int n = arr.length;
        for (int i = 0; i < n; ++i)
            System.out.print(arr[i] + " ");
        System.out.println();
    }
 
    // Driver method to test above
    public static void main(String args[])
    {
        BubbleSort ob = new BubbleSort();
        int arr[] = { 64, 34, 25, 12, 22, 11, 90 };
        ob.bubbleSort(arr);
        System.out.println("Sorted array");
        ob.printArray(arr);
    }
}
/* This code is contributed by Rajat Mishra */

Python3




# Python program for implementation of Bubble Sort
 
 
def bubbleSort(arr):
    n = len(arr)
 
    # Traverse through all array elements
    for i in range(n):
 
        # Last i elements are already in place
        for j in range(0, n-i-1):
 
            # traverse the array from 0 to n-i-1
            # Swap if the element found is greater
            # than the next element
            if arr[j] > arr[j+1]:
                arr[j], arr[j+1] = arr[j+1], arr[j]
 
 
# Driver code to test above
arr = [64, 34, 25, 12, 22, 11, 90]
 
bubbleSort(arr)
 
print("Sorted array is:")
for i in range(len(arr)):
    print("%d" % arr[i], end=" ")

C#




// C# program for implementation
// of Bubble Sort
using System;
 
class GFG {
    static void bubbleSort(int[] arr)
    {
        int n = arr.Length;
        for (int i = 0; i < n - 1; i++)
            for (int j = 0; j < n - i - 1; j++)
                if (arr[j] > arr[j + 1]) {
                    // swap temp and arr[i]
                    int temp = arr[j];
                    arr[j] = arr[j + 1];
                    arr[j + 1] = temp;
                }
    }
 
    /* Prints the array */
    static void printArray(int[] arr)
    {
        int n = arr.Length;
        for (int i = 0; i < n; ++i)
            Console.Write(arr[i] + " ");
        Console.WriteLine();
    }
 
    // Driver method
    public static void Main()
    {
        int[] arr = { 64, 34, 25, 12, 22, 11, 90 };
        bubbleSort(arr);
        Console.WriteLine("Sorted array");
        printArray(arr);
    }
}
 
// This code is contributed by Sam007

PHP




<?php
// PHP program for implementation
// of Bubble Sort
 
function bubbleSort(&$arr)
{
    $n = sizeof($arr);
 
    // Traverse through all array elements
    for($i = 0; $i < $n; $i++)
    {
        // Last i elements are already in place
        for ($j = 0; $j < $n - $i - 1; $j++)
        {
            // traverse the array from 0 to n-i-1
            // Swap if the element found is greater
            // than the next element
            if ($arr[$j] > $arr[$j+1])
            {
                $t = $arr[$j];
                $arr[$j] = $arr[$j+1];
                $arr[$j+1] = $t;
            }
        }
    }
}
 
// Driver code to test above
$arr = array(64, 34, 25, 12, 22, 11, 90);
 
$len = sizeof($arr);
bubbleSort($arr);
 
echo "Sorted array : \n";
 
for ($i = 0; $i < $len; $i++)
    echo $arr[$i]." ";
 
// This code is contributed by ChitraNayal.
?>

Javascript




<script>
 
function swap(arr, xp, yp)
{
    var temp = arr[xp];
    arr[xp] = arr[yp];
    arr[yp] = temp;
}
 
// An optimized version of Bubble Sort
function bubbleSort( arr, n)
{
var i, j;
for (i = 0; i < n-1; i++)
{
    for (j = 0; j < n-i-1; j++)
    {
        if (arr[j] > arr[j+1])
        {
        swap(arr,j,j+1);
         
        }
    }
 
}
}
 
/* Function to print an array */
function printArray(arr, size)
{
    var i;
    for (i=0; i < size; i++)
        document.write(arr[i]+ " ");
    document.write("\n");
}
 
// Driver program to test above functions
  var arr = [64, 34, 25, 12, 22, 11, 90];
    var n = 7;
    document.write("UnSorted array: \n");
    printArray(arr, n);
 
    bubbleSort(arr, n);
    document.write("Sorted array: \n");
    printArray(arr, n);
 
 
</script>
Output
Sorted array: 
1 2 4 5 8 

Optimized Implementation of Bubble Sort: 

  • The above function always runs O(n^2) time even if the array is sorted.
  • It can be optimized by stopping the algorithm if the inner loop didn’t cause any swap. 

Below is the implementation for the above approach: 

C++




// Optimized implementation of Bubble sort
#include <bits/stdc++.h>
using namespace std;
 
// An optimized version of Bubble Sort
void bubbleSort(int arr[], int n)
{
   int i, j;
   bool swapped;
   for (i = 0; i < n-1; i++)
   {
     swapped = false;
     for (j = 0; j < n-i-1; j++)
     {
        if (arr[j] > arr[j+1])
        {
           swap(arr[j], arr[j+1]);
           swapped = true;
        }
     }
 
     // IF no two elements were swapped
     // by inner loop, then break
     if (swapped == false)
        break;
   }
}
 
// Function to print an array
void printArray(int arr[], int size)
{
    int i;
    for (i = 0; i < size; i++)
        cout <<" "<< arr[i];
}
 
// Driver program to test above functions
int main()
{
    int arr[] = {5, 3, 1, 9, 8, 2, 4, 7};
    int N = sizeof(arr)/sizeof(arr[0]);
    bubbleSort(arr, N);
    cout <<"Sorted array: \n";
    printArray(arr, N);
    return 0;
}
// This code is contributed by shivanisinghss2110

C




// Optimized implementation of Bubble sort
#include <stdio.h>
#include <stdbool.h>
 
void swap(int *xp, int *yp)
{
    int temp = *xp;
    *xp = *yp;
    *yp = temp;
}
 
// An optimized version of Bubble Sort
void bubbleSort(int arr[], int n)
{
   int i, j;
   bool swapped;
   for (i = 0; i < n-1; i++)
   {
     swapped = false;
     for (j = 0; j < n-i-1; j++)
     {
        if (arr[j] > arr[j+1])
        {
           swap(&arr[j], &arr[j+1]);
           swapped = true;
        }
     }
 
     // IF no two elements were swapped by inner loop, then break
     if (swapped == false)
        break;
   }
}
 
/* Function to print an array */
void printArray(int arr[], int size)
{
    int i;
    for (i=0; i < size; i++)
        printf("%d ", arr[i]);
    printf("n");
}
 
// Driver program to test above functions
int main()
{
    int arr[] = {64, 34, 25, 12, 22, 11, 90};
    int n = sizeof(arr)/sizeof(arr[0]);
    bubbleSort(arr, n);
    printf("Sorted array: \n");
    printArray(arr, n);
    return 0;
}

Java




// Optimized java implementation
// of Bubble sort
import java.io.*;
 
class GFG
{
    // An optimized version of Bubble Sort
    static void bubbleSort(int arr[], int n)
    {
        int i, j, temp;
        boolean swapped;
        for (i = 0; i < n - 1; i++)
        {
            swapped = false;
            for (j = 0; j < n - i - 1; j++)
            {
                if (arr[j] > arr[j + 1])
                {
                    // swap arr[j] and arr[j+1]
                    temp = arr[j];
                    arr[j] = arr[j + 1];
                    arr[j + 1] = temp;
                    swapped = true;
                }
            }
 
            // IF no two elements were
            // swapped by inner loop, then break
            if (swapped == false)
                break;
        }
    }
 
    // Function to print an array
    static void printArray(int arr[], int size)
    {
        int i;
        for (i = 0; i < size; i++)
            System.out.print(arr[i] + " ");
        System.out.println();
    }
 
    // Driver program
    public static void main(String args[])
    {
        int arr[] = { 64, 34, 25, 12, 22, 11, 90 };
        int n = arr.length;
        bubbleSort(arr, n);
        System.out.println("Sorted array: ");
        printArray(arr, n);
    }
}
 
 
// This code is contributed
// by Nikita Tiwari.

Python3




# Python3 Optimized implementation
# of Bubble sort
 
# An optimized version of Bubble Sort
def bubbleSort(arr):
    n = len(arr)
  
    # Traverse through all array elements
    for i in range(n):
        swapped = False
 
        # Last i elements are already
        #  in place
        for j in range(0, n-i-1):
  
            # traverse the array from 0 to
            # n-i-1. Swap if the element
            # found is greater than the
            # next element
            if arr[j] > arr[j+1] :
                arr[j], arr[j+1] = arr[j+1], arr[j]
                swapped = True
 
        # IF no two elements were swapped
        # by inner loop, then break
        if swapped == False:
            break
          
# Driver code to test above
arr = [64, 34, 25, 12, 22, 11, 90]
  
bubbleSort(arr)
  
print ("Sorted array :")
for i in range(len(arr)):
    print ("%d" %arr[i],end=" ")
 
# This code is contributed by Shreyanshi Arun

C#




// Optimized C# implementation
// of Bubble sort
using System;
 
class GFG
{
    // An optimized version of Bubble Sort
    static void bubbleSort(int []arr, int n)
    {
        int i, j, temp;
        bool swapped;
        for (i = 0; i < n - 1; i++)
        {
            swapped = false;
            for (j = 0; j < n - i - 1; j++)
            {
                if (arr[j] > arr[j + 1])
                {
                    // swap arr[j] and arr[j+1]
                    temp = arr[j];
                    arr[j] = arr[j + 1];
                    arr[j + 1] = temp;
                    swapped = true;
                }
            }
 
            // IF no two elements were
            // swapped by inner loop, then break
            if (swapped == false)
                break;
        }
    }
 
    // Function to print an array
    static void printArray(int []arr, int size)
    {
        int i;
        for (i = 0; i < size; i++)
            Console.Write(arr[i] + " ");
        Console.WriteLine();
    }
 
    // Driver method
    public static void Main()
    {
        int []arr = {64, 34, 25, 12, 22, 11, 90};
        int n = arr.Length;
        bubbleSort(arr,n);
        Console.WriteLine("Sorted array");
        printArray(arr,n);
    }
 
}
// This code is contributed by Sam007

PHP




<?php
// PHP Optimized implementation
// of Bubble sort
 
// An optimized version of Bubble Sort
function bubbleSort(&$arr)
{
    $n = sizeof($arr);
 
    // Traverse through all array elements
    for($i = 0; $i < $n; $i++)
    {
        $swapped = False;
 
        // Last i elements are already
        // in place
        for ($j = 0; $j < $n - $i - 1; $j++)
        {
             
            // traverse the array from 0 to
            // n-i-1. Swap if the element
            // found is greater than the
            // next element
            if ($arr[$j] > $arr[$j+1])
            {
                $t = $arr[$j];
                $arr[$j] = $arr[$j+1];
                $arr[$j+1] = $t;
                $swapped = True;
            }
        }
 
        // IF no two elements were swapped
        // by inner loop, then break
        if ($swapped == False)
            break;
    }
}
         
// Driver code to test above
$arr = array(64, 34, 25, 12, 22, 11, 90);
$len = sizeof($arr);
bubbleSort($arr);
 
echo "Sorted array : \n";
 
for($i = 0; $i < $len; $i++)
    echo $arr[$i]." ";
     
// This code is contributed by ChitraNayal.
?>

Javascript




<script>
 
// Optimized javaScript implementation
// of Bubble sort
// An optimized version of Bubble Sort
function bubbleSort(arr, n)
    {
        var i, j, temp;
        var swapped;
        for (i = 0; i < n - 1; i++)
        {
            swapped = false;
            for (j = 0; j < n - i - 1; j++)
            {
                if (arr[j] > arr[j + 1])
                {
                    // swap arr[j] and arr[j+1]
                    temp = arr[j];
                    arr[j] = arr[j + 1];
                    arr[j + 1] = temp;
                    swapped = true;
                }
            }
 
            // IF no two elements were
            // swapped by inner loop, then break
            if (swapped == false)
                break;
        }
    }
 
    // Function to print an array
    function printArray(arr, size)
    {
        var i;
        for (i = 0; i < size; i++)
            document.write(arr[i] + " ");
        document.writeln();
    }
 
    // Driver program
        var arr = [ 64, 34, 25, 12, 22, 11, 90 ];
        var n = arr.length;
        bubbleSort(arr, n);
        document.write("Sorted array: ");
        printArray(arr, n);
 
// This code is contributed shivanisinghss2110
</script>
Output
Sorted array: 
 1 2 3 4 5 7 8 9

Time Complexity: O(N2)
Auxiliary Space: O(1)

Worst Case Analysis for Bubble Sort:

The worst-case condition for bubble sort occurs when elements of the array are arranged in decreasing order.
In the worst case, the total number of iterations or passes required to sort a given array is (n-1). where ‘n’ is a number of elements present in the array.

  At pass 1 :  Number of comparisons = (n-1)
                     Number of swaps = (n-1)

  At pass 2 :  Number of comparisons = (n-2)
                     Number of swaps = (n-2)

  At pass 3 :  Number of comparisons = (n-3)
                    Number of swaps = (n-3)
                              .
                              .
                              .
  At pass n-1 :  Number of comparisons = 1
                        Number of swaps = 1

Now , calculating total number of comparison required to sort the array
= (n-1) + (n-2) +  (n-3) + . . . 2 + 1
= (n-1)*(n-1+1)/2  { by using sum of N natural Number formula }
= n (n-1)/2    

For Worst case:

Total number of swaps = Total number of comparison
Total number of comparison (Worst case) = n(n-1)/2
Total number of swaps (Worst case) = n(n-1)/2

Worst and Average Case Time Complexity: O(N2). The worst case occurs when an array is reverse sorted.

Best Case Time Complexity: O(N). The best case occurs when an array is already sorted.

Auxiliary Space: O(1)

What is the Boundary Case for Bubble sort? 

Bubble sort takes minimum time (Order of n) when elements are already sorted. Hence it is best to check if the array is already sorted or not beforehand, to avoid O(N2) time complexity.

Does sorting happens in place in Bubble sort?

Yes, Bubble sort performs swapping of adjacent pairs without use of any major data structure. Hence Bubble sort algorithm is an in-place algorithm.

Is Bubble sort algorithm stable?

Yes, bubble sort algorithm is stable.

Where is Bubble sort algorithm used?

Due to its simplicity, bubble sort is often used to introduce the concept of a sorting algorithm. 
In computer graphics, it is popular for its capability to detect a very small error (like a swap of just two elements) in almost-sorted arrays and fix it with just linear complexity (2n). 

For example, it is used in a polygon filling algorithm, where bounding lines are sorted by their x coordinate at a specific scan line (a line parallel to x-axis) and with incrementing y their order changes (two elements are swapped) only at intersections of two lines (Source: Wikipedia)
  

Snapshots: Quiz on Bubble Sort

Other Sorting Algorithms on GeeksforGeeks/GeeksQuiz: 
Recursive Bubble Sort
Coding practice for sorting.


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