Added 25 solutions

Java/Object Oriented Programming/Java Interface/Solution.java

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+//     Author: Rodney Shaghoulian
+//     Github: github.com/rshaghoulian
+// HackerRank: hackerrank.com/rshaghoulian
+
+import java.util.*;
+
+interface AdvancedArithmetic {
+    int divisor_sum(int n);
+}
+
+class MyCalculator implements AdvancedArithmetic {
+    //          Runtime: 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);
+        }
+    }
+}