Hackerrank Java Substring Comparisons

Hackerrank Java Substring Comparisons

import java.util.Scanner;
public class Solution {
public static String getSmallestAndLargest(String s, int k) {
        String smallest = "";
        String largest = "";
        smallest = s.substring(0,k);
        largest = s.substring(0,k);
//         "Compare to" method doesn't turn just the equel case it also turns a value.
        for(int i=0; i<=s.length()-k; i++ ){
            String str = s.substring(i,k+i);
            if (smallest.compareTo(str)>0){
                smallest = str;
            }
            if(largest.compareTo(str)<0){
                largest=str;
            }
        }  
        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));
    }
}

My solution:

package org.redbull4.helloworld;

import java.util.*;

public class Hello {
    static Scanner sc = new Scanner(System.in);

    public static String getSmallestAndLargest(String s, int k) {
        String _String = "", smallest = s.substring(0, k),
                largest = s.substring(0, k), output = "";

        for (int i = 0; i < s.length(); i++) {
            if (i + k > s.length())
                break;

            _String += s.substring(i, i + k);

            if (smallest.compareTo(_String) > 0)
                smallest = _String;
            if (largest.compareTo(_String) < 0)
                largest = _String;

            _String = "";
        }

        output = smallest + '\n' + largest;

        return output;
    }

    public static void main(String[] args) {
        String s = sc.nextLine();
        int k = sc.nextInt();

        System.out.println(getSmallestAndLargest(s, k));
    }
}

Should be
String smallest = s.substring(0,k+1);
String largest = s.substring(s.length()-k);

Do anyone have list of all test cases ?
String Comparision Java - HackerRank

we save one iteration by using i=1 instead of i=0;

What about this?

public static String getSmallestAndLargest(String s, int k) {
		List<String> subs = new ArrayList<>();
		for (int i = 0; i < s.length(); i++) {
			if (k > s.length()) {
				break;
			}
			subs.add( s.substring(i, k));
			k++;
		}
		subs = subs.stream().sorted().collect(Collectors.toList());
		return subs.get(0) + "\n" + subs.get(subs.size() - 1);
	}

public static String getSmallestAndLargest(String s, int k) {
String smallest = "";
String largest = "";

    ArrayList<String> st = new ArrayList<>();
    int s_len = s.length();
    for (int i =0; i<=s_len-k; i++){
        String sk = s.substring(i,i+k);
        st.add(sk);
    }
   
    smallest = Collections.min(st);
    largest = Collections.max(st);

    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));
}