Cynthia digital root

[CynthiaTerrazas]

In this kata, you must create a digital root function.

A digital root is the recursive sum of all the digits in a number. Given n, take the sum of the digits of n. If that value has two digits, continue reducing in this way until a single-digit number is produced. This is only applicable to the natural numbers.

Here's how it works (Ruby example given):

digital_root(16)
=> 1 + 6
=> 7

digital_root(942)
=> 9 + 4 + 2
=> 15 ...
=> 1 + 5
=> 6

digital_root(132189)
=> 1 + 3 + 2 + 1 + 8 + 9
=> 24 ...
=> 2 + 4
=> 6

digital_root(493193)
=> 4 + 9 + 3 + 1 + 9 + 3
=> 29 ...
=> 2 + 9
=> 11 ...
=> 1 + 1
=> 2

[codecov-io]

Codecov Report

Merging #157 into develop will increase coverage by 0.59%.
The diff coverage is 100%.

@@              Coverage Diff              @@
##             develop     #157      +/-   ##
=============================================
+ Coverage      88.39%   88.98%   +0.59%     
- Complexity       492      524      +32     
=============================================
  Files            109      117       +8     
  Lines           1043     1099      +56     
  Branches         178      195      +17     
=============================================
+ Hits             922      978      +56     
  Misses           106      106              
  Partials          15       15

Impacted Files	Coverage Δ	Complexity Δ
.../org/fundacionjala/coding/cynthia/DigitalRoot.java	100% <100%> (ø)	4 <4> (?)
...n/java/org/fundacionjala/coding/yury/Frequent.java	100% <0%> (ø)	6% <0%> (?)
...org/fundacionjala/coding/richard/MostFrequent.java	100% <0%> (ø)	7% <0%> (?)
...rg/fundacionjala/coding/cynthia/SumOddNumbers.java	100% <0%> (ø)	2% <0%> (?)
...org/fundacionjala/coding/ovidio/CountingSheep.java	100% <0%> (ø)	2% <0%> (?)
.../java/org/fundacionjala/coding/ovidio/Persist.java	100% <0%> (ø)	4% <0%> (?)
...n/java/org/fundacionjala/coding/ovidio/Vowels.java	100% <0%> (ø)	4% <0%> (?)
...in/java/org/fundacionjala/coding/ovidio/DRoot.java	100% <0%> (ø)	3% <0%> (?)
...a/org/fundacionjala/coding/yury/EanValidation.java	88.88% <0%> (+3.17%)	5% <0%> (ø)	⬇️

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[carledriss]

This should be

res += mod;

[carledriss]

Please update this
expectedResult is first than actualResult. :)

[carledriss]

In order to avoid some unnecessary variables.
Try this.

    public int sumOfDigits(int num) {
        int res = 0;
        while (num != 0) {
            res += num % 10;
            num = num / 10;
        }
        return res >= 10 ? sumOfDigits(res) : res;
    }