Sorting: Bubble Sort

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]);
        }
    }
    
}

Task 
Given an -element array, , of distinct elements, sort 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.

Input Format

The first line contains an integer, , denoting the number of elements in array . 
The second line contains  space-separated integers describing the respective values of .

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.

풀이

기본적으로 버블정렬에 대해 알고 있다면 쉽게 풀 수 있을 것이다.

시간복잡도가 O(n^2) 이다보니 실제 잘 사용하는 정렬은 아니나, 쓰기 매우 간편하다는 장점이 있다.

package algorithms;

import java.util.Scanner;

public class BubbleSort {

    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        int n = in.nextInt();
        int a[] = new int[n];
        for(int a_i=0; a_i < n; a_i++){
            a[a_i] = in.nextInt();
        }

        int count = 0;
        for(int i = 0; i < a.length; i++){
            for(int j = 0; j < a.length - 1; j++){
                if(a[j] > a[j+1]){
                    int tmp = a[j+1];
                    a[j+1] = a[j];
                    a[j] = tmp;
                    count++;
                }
            }
        }
        System.out.println("Array is sorted in " + count + " swaps.");
        System.out.println("First Element: " + a[0]);
        System.out.println("Last Element: " + a[a.length-1]);
    }
}