Microsoft screening question

Round 1

Questions: Write a function: public String solution();
that returns a string made of digits for which the following calculate function returns the highest possible value:

import java.util.Arrays;

public class Solution {
    
    public int calculate(String S) {
        
        int length = S.length();
        if (length > 100) {
            return 0; 
        }

        int[] count = new int[100];

        for (int i = 0; i < length - 1; i++) {
            int num = Integer.parseInt(S.substring(i, i + 1));
            count[num] = 1;
        }

        return Arrays.stream(count).sum();
    }
}

returned value | score
----------------+-------
>= 59 | 50
>= 64 | 55
>= 69 | 60
>= 74 | 65
>= 79 | 70
>= 84 | 75
>= 89 | 80
>= 94 | 90
>= 99 | 100

Do not modify the calculate method.