Solving the kata sum fct

src/main/java/org/fundacionjala/coding/abel/SumFct.java

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+package org.fundacionjala.coding.abel;
+
+import java.math.BigInteger;
+
+/**
+ * The drawing shows 6 squares the sides of which have a length of 1, 1, 2, 3, 5, 8. It's easy to see that
+ * the sum of the perimeters of these squares is : 4 * (1 + 1 + 2 + 3 + 5 + 8) = 4 * 20 = 80
+ * Could you give the sum of the perimeters of all the squares in a rectangle when there are n + 1 squares
+ * disposed in the same manner as in the drawing:
+ * #Hint: See Fibonacci sequence
+ * #Ref: http://oeis.org/A000045
+ * The function perimeter has for parameter n where n + 1 is the number of squares (they are numbered from 0 to n)
+ * and returns the total perimeter of all the squares.
+ */
+public final class SumFct {
+
+    /**
+     * Private Constructor.
+     */
+    private SumFct() {
+
+    }
+
+    /**
+     * Calculates the permiter of a rectangle compose by squares.
+     *
+     * @param n Number of rectanbles.
+     * @return Big Integer.
+     */
+    public static BigInteger perimeter(BigInteger n) {
+        BigInteger a;
+        BigInteger b = BigInteger.ONE;
+        BigInteger c = BigInteger.ONE;
+        BigInteger total = BigInteger.ZERO;
+
+        for (int i = 0; i <= n.intValue(); i++) {
+            a = b;
+            b = c;
+            c = a.add(b);
+            total = total.add(a);
+        }
+
+        return total.multiply(BigInteger.valueOf(4));
+    }
+}

src/test/java/org/fundacionjala/coding/abel/SumFctTest.java

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+package org.fundacionjala.coding.abel;
+
+import java.lang.reflect.Constructor;
+import java.lang.reflect.InvocationTargetException;
+import java.lang.reflect.Modifier;
+import java.math.BigInteger;
+
+import org.junit.Test;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertTrue;
+
+/**
+ * Created by abelb on 8/23/2017.
+ */
+public class SumFctTest {
+
+    /**
+     * Test for Private Constructors.
+     *
+     * @throws NoSuchMethodException     Thrown when a particular method cannot be found.
+     * @throws IllegalAccessException    Thrown when an application tries to reflectively create an instance.
+     * @throws InvocationTargetException thrown by an invoked method or constructor.
+     * @throws InstantiationException    Thrown when an application tries to create an instance of a class
+     *                                   using the {@code newInstance} method in class.
+     */
+    @Test
+    public void privateConstructorTest() throws NoSuchMethodException, IllegalAccessException,
+            InvocationTargetException, InstantiationException {
+        Constructor<SumFct> constructor = SumFct.class.getDeclaredConstructor();
+        assertTrue(Modifier.isPrivate(constructor.getModifiers()));
+        constructor.setAccessible(true);
+        constructor.newInstance();
+    }
+
+    /**
+     * Provided test.
+     */
+    @Test
+    public void test1() {
+        assertEquals(BigInteger.valueOf(80), SumFct.perimeter(BigInteger.valueOf(5)));
+    }
+
+    /**
+     * Provided test.
+     */
+    @Test
+    public void test2() {
+        assertEquals(BigInteger.valueOf(216), SumFct.perimeter(BigInteger.valueOf(7)));
+    }
+
+    /**
+     * Provided test.
+     */
+    @Test
+    public void test3() {
+        assertEquals(BigInteger.valueOf(14098308), SumFct.perimeter(BigInteger.valueOf(30)));
+    }
+}