HackerRank-Solutions/Java/Object Oriented Programming/Java Interface/Solution.java

//     Author: Rodney Shaghoulian
//     Github: github.com/RodneyShag
// HackerRank: hackerrank.com/RodneyShag

import java.util.*;

interface AdvancedArithmetic {
    int divisor_sum(int n);
}

class MyCalculator implements AdvancedArithmetic {
    //  Time Complexity: O(n^(1/2))
    // Space Complexity: O(1)
    public int divisor_sum(int n) {
        int sum  = 0;
        int sqrt = (int) Math.sqrt(n);
        for (int i = 1; i <= sqrt; i++) {
            if (n % i == 0) { // if "i" is a divisor
                sum += i + n/i; // add both divisors
            }
        }
        /* If sqrt is a divisor, we should only count it once */
        if (sqrt * sqrt == n) {
            sum -= sqrt;
        }
        return sum;
    }
}

class Solution {
    public static void main(String[] args) {
        MyCalculator my_calculator = new MyCalculator();
        System.out.print("I implemented: ");
        ImplementedInterfaceNames(my_calculator);
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        System.out.print(my_calculator.divisor_sum(n) + "\n");
        sc.close();
    }
    /*
     *  ImplementedInterfaceNames method takes an object and prints the name of the interfaces it implemented
     */
    static void ImplementedInterfaceNames(Object o) {
        Class[] theInterfaces = o.getClass().getInterfaces();
        for (int i = 0; i < theInterfaces.length; i++) {
            String interfaceName = theInterfaces[i].getName();
            System.out.println(interfaceName);
        }
    }
}