Add AliquotSum (#3765)

src/main/java/com/thealgorithms/maths/AliquotSum.java

@@ -30,4 +30,35 @@ public class AliquotSum {
 
         return sumWrapper.value;
     }
+    
+     /**
+     * Function to calculate the aliquot sum of an integer number
+     *
+     * @param n a positive integer
+     * @return aliquot sum of given {@code number}
+     */
+    public static int getAliquotSum(int n) {
+        if (n <= 0)
+            return -1;
+        int sum = 1;
+        double root = Math.sqrt(n);
+        /*
+         * We can get the factors after the root by dividing number by its factors
+         * before the root.
+         * Ex- Factors of 100 are 1, 2, 4, 5, 10, 20, 25, 50 and 100.
+         * Root of 100 is 10. So factors before 10 are 1, 2, 4 and 5.
+         * Now by dividing 100 by each factor before 10 we get:
+         * 100/1 = 100, 100/2 = 50, 100/4 = 25 and 100/5 = 20
+         * So we get 100, 50, 25 and 20 which are factors of 100 after 10
+         */
+        for (int i = 2; i <= root; i++) {
+            if (n % i == 0) {
+                sum += i + n / i;
+            }
+        }
+        // if n is a perfect square then its root was added twice in above loop, so subtracting root from sum
+        if (root == (int) root)
+            sum -= root;
+        return sum;
+    }
 }

src/test/java/com/thealgorithms/maths/AliquotSumTest.java

@@ -12,5 +12,9 @@ public class AliquotSumTest {
         assertEquals(6, AliquotSum.getAliquotValue(6));
         assertEquals(9, AliquotSum.getAliquotValue(15));
         assertEquals(1, AliquotSum.getAliquotValue(19));
+        assertEquals(0, AliquotSum.getAliquotSum(1));
+        assertEquals(6, AliquotSum.getAliquotSum(6));
+        assertEquals(9, AliquotSum.getAliquotSum(15));
+        assertEquals(1, AliquotSum.getAliquotSum(19));
     }
 }