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+%0A// https://www.hackerrank.com/contests/30-days-of-code/challenges/day-19-interfaces/submissions/code/4760172%0A%0Aclass Calculator implements AdvancedArithmetic %7B%0A    %0A    public int divisorSum(int n) %7B%0A        Set%3CInteger%3E divisors = divisors(n);%0A        %0A        int sum = 0;%0A        for (Integer i : divisors)%0A            sum += i;%0A        %0A        return sum;%0A    %7D%0A    %0A    private Set%3CInteger%3E divisors(int n) %7B%0A        Set%3CInteger%3E divisors = new HashSet%3CInteger%3E();%0A        %0A        divisors.add(1);%0A        divisors.add(n);%0A        %0A        for (int i = 2; i*i %3C= n; ++i) %7B%0A            if (n %25 i == 0) %7B%0A                divisors.add(i);%0A                divisors.add(n / i);%0A            %7D%0A        %7D%0A        %0A        return divisors;%0A    %7D%0A    %0A    %0A%7D%0A

Create Day19-Interfaces.java