Sorting: Bubble Sort - Hacker Rank Solution

Check out the resources on the page's right side to learn more about bubble sort. The video tutorial is by Gayle Laakmann McDowell, author of the best-selling interview book Cracking the Coding Interview.

Consider the following version of Bubble Sort:

for (int i = 0; i < n; i++) {
    
    for (int j = 0; j < n - 1; j++) {
        // Swap adjacent elements if they are in decreasing order
        if (a[j] > a[j + 1]) {
            swap(a[j], a[j + 1]);
        }
    }
    
}

Given an array of integers, sort the array in ascending order using the Bubble Sort algorithm above. Once sorted, print the following three lines:

1. Array is sorted in numSwaps swaps., where  is the number of swaps that took place.
2. First Element: firstElement, where  is the first element in the sorted array.
3. Last Element: lastElement, where  is the last element in the sorted array.

Hint: To complete this challenge, you must add a variable that keeps a running tally of all swaps that occur during execution.

For example, given a worst-case but small array to sort:  we go through the following steps:

swap    a       
0       [6,4,1]
1       [4,6,1]
2       [4,1,6]
3       [1,4,6]

It took  swaps to sort the array. Output would be

Array is sorted in 3 swaps.  
First Element: 1  
Last Element: 6  

Function Description

Complete the function countSwaps in the editor below. It should print the three lines required, then return.

countSwaps has the following parameter(s):

• a: an array of integers .

Input Format

The first line contains an integer, , the size of the array . 
The second line contains  space-separated integers .

Constraints

Output Format

You must print the following three lines of output:

1. Array is sorted in numSwaps swaps., where  is the number of swaps that took place.
2. First Element: firstElement, where  is the first element in the sorted array.
3. Last Element: lastElement, where  is the last element in the sorted array.

Sample Input 0

3
1 2 3

Sample Output 0

Array is sorted in 0 swaps.
First Element: 1
Last Element: 3

Explanation 0 
The array is already sorted, so  swaps take place and we print the necessary three lines of output shown above.

Sample Input 1

3
3 2 1

Sample Output 1

Array is sorted in 3 swaps.
First Element: 1
Last Element: 3

Explanation 1 
The array is not sorted, and its initial values are: . The following  swaps take place:

At this point the array is sorted and we print the necessary three lines of output shown above.

Sorting: Bubble Sort - Hacker Rank Solution

Bubble sort is  approach to sort an array. At every iteration we try to put the maximum element in range  at position where . There are a total of  elements, so if we run this iteration  times we are done. The below is the code snippet for the idea above.

for (int i = 0; i < n; i++) {
    for (int j = 0; j < n - 1; j++) {
        // Swap adjacent elements if they are in decreasing order
        if (a[j] > a[j + 1]) {
            swap(a[j], a[j + 1]);
        }
    }  
}

To query how many times we have swapped the elements, we can just keep track of a counter and increment it by  whenever we swap the elements in the code above.

Problem Setter's code:

void countSwaps(vector<int> a) {
    int cnt=0;
    int n=a.size();
    for(int i=0;i<n;i++)
    {
        for(int j=0;j<n-1;j++)
        {
            if(a[j]>a[j+1])
            {
                swap(a[j],a[j+1]);
                cnt++;
            }
        }
    }
    cout<<"Array is sorted in "<<cnt<<" swaps."<<endl;
    cout<<"First Element: "<<a[0]<<endl;
    cout<<"Last Element: "<<a[a.size()-1]<<endl;
}

Problem Tester's code:

Java

import java.util.Scanner;

public class Solution {
    private static int[] array;

    private static void bubbleSort() {
        int n = array.length;
        
        // number of swaps for all array iterations
        int totalSwaps = 0; 

        for (int i = 0; i < n; i++) {
            // number of swaps for current array iteration
            int numSwaps = 0;
            
            for (int j = 0; j < array.length - 1; j++) {
                if (array[j] > array[j + 1]) {
                    int tmp = array[j];
                    array[j] = array[j + 1];
                    array[j + 1] = tmp;
                    numSwaps++; 
                    totalSwaps++;
                }
            }

            if (numSwaps == 0) {
                System.out.printf("Array is sorted in %d swaps.\n", totalSwaps);
                System.out.printf("First Element: %d\n", array[0]);
                System.out.printf("Last Element: %d\n", array[n - 1]);
                
                break;
            }
        }
    }
    
    public static void main(String[] args){
        Scanner in = new Scanner(System.in);
        int n = in.nextInt();
        array = new int[n];
        for (int i = 0; i < n; i++) {
            array[i] = in.nextInt();
        }
        in.close();

        bubbleSort();
    }
}

Python 3

import sys

n = int(input())
a = [int(i) for i in input().strip().split(' ')]
numSwaps = 0

for i in range(n):
    currentSwaps = 0

    for j in range(0, n - 1):
        if a[j] > a[j + 1]:
            a[j], a[j + 1] = a[j + 1], a[j]
            currentSwaps += 1
            
    numSwaps += currentSwaps
            
    if currentSwaps == 0:
        break
        
print("Array is sorted in " + str(numSwaps) + " swaps.")
print("First Element: " + str(a[0]))
print("Last Element: " + str(a[-1]))