HackerRank Java Substring Comparisons problem solution

In this HackerRank java substring comparisons problem in the java programming language you have Given a string, s, and an integer, k, complete the function so that it finds the lexicographically smallest and largest substrings of length k.

HackerRank java substring comparisons problem solution.

import java.util.Scanner;

public class Solution {

    public static String getSmallestAndLargest(String s, int k) {
        String smallest = "";
        String largest = "";
        
        java.util.List<String> a = new java.util.ArrayList<>();

        for(int i=0;i<s.length()-k+1;i++){
                a.add(s.substring(i,i+k));   
        }
        java.util.Collections.sort(a);
         smallest = a.get(0);
         largest = a.get(a.size()-1);
        return smallest + "n" + largest;
    }


    public static void main(String[] args) {
        Scanner scan = new Scanner(System.in);
        String s = scan.next();
        int k = scan.nextInt();
        scan.close();
      
        System.out.println(getSmallestAndLargest(s, k));
    }
}

Second solution

import java.io.*;
import java.util.*;
import java.text.*;
import java.math.*;
import java.util.regex.*;

public class Solution {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        String line = scanner.nextLine();
        int k = scanner.nextInt();
        String minSubstring = line.substring(0,k);
        String maxSubstring = line.substring(0,k);
        for (int i = 1; i < line.length()-k+1; i++) {
            String sub = line.substring(i,i+k);
            if (sub.compareTo(minSubstring) < 0) {
                minSubstring = sub;
            }
            if (sub.compareTo(maxSubstring) > 0) {
                maxSubstring = sub;
            }
        }
        System.out.println(minSubstring);
        System.out.println(maxSubstring);
    }
}