How to include 0s of substrings without ArrayList and array?

October 30, 2022

I finished a program where I use Math.random() to pick a number 25-50, both inclusive. This will be passed to stringAdd() as length. The method creates a string with the randomized length from numbers 0-9 (also inclusive) using Math.random() as well.

Then, if the length is above 30, "group" the string by 3 digits, otherwise, just "group" by 2 digits. Uneven grouping is allowed at the end (see the sample output I included below).

Last, the program must loop through the string, change all group of numbers to int and then add the sum to a total, so the total can be returned.

This is the code I have:

public class Grouping
{
    public static int stringAdd(int length)
    {
        ArrayList<String> numbers = new ArrayList<String>();
        String randomString = "";
        for(int i = 0; i < length; i++)
    {
        int randomNumbers = (int)(Math.random()*10);
        randomString = randomString + randomNumbers;
    }
    System.out.println("Generated string: " + randomString);
        
    int group = 2;
    if(length > 30)
        group = 3;
        
    for(int i = 0; i < length; i = i + group)
    {
        numbers.add(randomString.substring(i, Math.min(length, i + group)));
            System.out.println("Group: " + randomString.substring(i, Math.min(length, i + group)));
    }
        
        int[] array = new int[numbers.size()];
        int total = 0;
        
    for(int i = 0; i < numbers.size(); i++)
    {
        array[i] = Integer.parseInt(numbers.get(i));
            total = total + array[i];
    }
    return total;
    }

    public static void main(String[] args)
    {
    int randomLength = (int)(Math.random() * (50 - 25) + 1) + 25;
    System.out.println("Length of the string is " + randomLength);
    System.out.println("Total: " + stringAdd(randomLength));
    }
}

The output is this:

Length of the string is 30
Generated string: 157768294302045453441313535692
Group: 15
Group: 77
Group: 68
Group: 29
Group: 43
Group: 02
Group: 04
Group: 54
Group: 53
Group: 44
Group: 13
Group: 13
Group: 53
Group: 56
Group: 92
Total: 616

However, I wanted to simplify this and remove the use of ArrayList and array so that I only need two for loops instead of three. So I did something similar that I already have:

int total = 0;
for(int i = 0; i < length; i = i + group)
{
   int digits = Integer.parseInt(randomString.substring(i, Math.min(length, i + group)));
   System.out.println("Group: " + digits);
   total = total + digits;
}
return total;

And one output is this, which looks fine…

Length of the string is 47
Generated string: 26011336670044862237923585625878411711193186128
Group: 260
Group: 113
Group: 366
Group: 700
Group: 448
Group: 622
Group: 379
Group: 235
Group: 856
Group: 258
Group: 784
Group: 117
Group: 111
Group: 931
Group: 861
Group: 28
Total: 7069

But another output would be this:

Length of the string is 28
Generated string: 7581863393306645423505929903
Group: 75
Group: 81
Group: 86
Group: 33
Group: 93
Group: 30
Group: 66
Group: 45
Group: 42
Group: 35
Group: 5
Group: 92
Group: 99
Group: 3
Total: 785

5 should actually be 05 and 3 should actually be 03. I understand that the "zero" in 03 does not add to the total, but I strictly want my program to group by the digits. I also am working under constraints so unfortunately I cannot use anything advanced yet

>Solution :

Numbers don’t have leading zeros. 3 is 03 is 003. If you require leading zeros, keep a string and only convert to a number when summing:

for(int i = 0; i < length; i = i + group)
{
   final String substring = randomString.substring(i, Math.min(length, i + group));
   System.out.println("Group: " + substring);
   int digits = Integer.parseInt(substring);
   total = total + digits;
}

for(int i = 0; i < length; i += group)
{
   final String digits = randomString.substring(i, Math.min(length, i + group));
   System.out.println("Group: " + digits);
   total += Integer.parseInt(digits);
}