The challenge

You must guess a sequence and it has something to do with the number given.

Example

x = 16

result = [1, 10, 11, 12, 13, 14, 15, 16, 2, 3, 4, 5, 6, 7, 8, 9]

The solution in Java code

Option 1:

import java.util.stream.IntStream;

class Challenge {
  static int[] sequence(int x) {
    return IntStream.rangeClosed(1, x)
                .mapToObj(String::valueOf)
                .sorted()
                .mapToInt(Integer::parseInt)
                .toArray();
  } 
}

Option 2:

import java.util.*;
class Challenge {
  static int[] sequence(int x) {
    String arr[] = new String[x];
    for(int i =1;i<=x;i++){
    arr[i-1]= ""+i;
    }
    Arrays.sort(arr);
    int[]  tor =  new int[x];
    for(int i = 0;i<x;i++){
      tor[i] = Integer.parseInt(arr[i]);
    }
    return tor ;
  }
  
}

Option 3:

class Challenge {
  public static int[] sequence(int x) {
    final var result = new int[x];
    int index = 0;
    for (int i = 1; i <= 9; i++) {
      result[index++] = i;
      for (int j = i * 10; j <= x && j < (i + 1) * 10; j++)
        result[index++] = j;
    }
    return result;
  } 
}

Test cases to validate our solution

import org.junit.Test;
import static org.junit.Assert.assertEquals;
import org.junit.runners.JUnit4;
import java.util.Arrays;

public class SolutionTest {
    @Test
    public void test0() {
        int[] result = {1, 10, 11, 12, 13, 14, 15, 16, 2, 3, 4, 5, 6, 7, 8, 9};
        int x = 16;
        String expected = Arrays.toString(result),
        actual = Arrays.toString(Challenge.sequence(x));
        assertEquals(expected, actual);
    }
    @Test
    public void test1() {
        int[] result = {1, 2, 3, 4, 5, 6, 7, 8, 9};
        int x = 9;
        String expected = Arrays.toString(result),
        actual = Arrays.toString(Challenge.sequence(x));
        assertEquals(expected, actual);
    }
}