Marcos_Kata_Magnet_Particules

src/main/java/org/fundacionjala/coding/marcos/Magnets.java

@@ -0,0 +1,48 @@
+package org.fundacionjala.coding.marcos;
+
+import java.util.stream.IntStream;
+
+/**
+ * Created by Marcos.
+ * <p>
+ * Professor Chambouliard hast just discovered a new type of magnet material.
+ * He put particles of this material in a box made of small boxes arranged
+ * in K rows and N columns as a kind of 2D matrix K x N where K and N are positive integers.
+ */
+
+public final class Magnets {
+
+    public static final int ONE = 1;
+    public static final int TWO = 2;
+
+    /**
+     * Private constructor for the Magnets utility class.
+     */
+    private Magnets() {
+
+    }
+
+    /**
+     * This method calculates the total force exerted by rows and columns using the
+     * kata summation equation.
+     *
+     * @param maxK max column value.
+     * @param maxN max row value.
+     * @return the summation result.
+     */
+    public static double doubles(int maxK, int maxN) {
+        return IntStream.rangeClosed(1, maxK).mapToDouble(k -> calculateForce(k, maxN)).sum();
+    }
+
+    /**
+     * This method calculates the total force exerted by a row using the Kata
+     * summation equation.
+     *
+     * @param k    fixed column value.
+     * @param maxN max row value.
+     * @return the summation result.
+     */
+    private static double calculateForce(int k, int maxN) {
+        return IntStream.rangeClosed(ONE, maxN).mapToDouble(n -> ONE / (k * Math.pow(n + ONE, TWO * k))).sum();
+    }
+}

src/test/java/org/fundacionjala/coding/marcos/MagnetsTest.java

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+package org.fundacionjala.coding.marcos;
+
+import java.lang.reflect.Constructor;
+import java.lang.reflect.InvocationTargetException;
+import java.lang.reflect.Modifier;
+import java.text.DecimalFormat;
+
+import org.junit.Test;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertTrue;
+
+/**
+ * Created by Marcos.
+ */
+public class MagnetsTest {
+
+    /**
+     * Custom assertion method for the kata.
+     *
+     * @param act actual result.
+     * @param exp expected result.
+     */
+    private static void assertFuzzyEquals(double act, double exp) {
+        boolean inRange = Math.abs(act - exp) <= 1e-6;
+        if (!inRange) {
+            DecimalFormat df = new DecimalFormat("#0.000000");
+            System.out.println("At 1e-6: Expected must be " + df.format(exp) + ", but got " + df.format(act));
+        }
+        assertEquals(true, inRange);
+    }
+
+    /**
+     * This test assert the modifier of the Sequence private constructor class.
+     *
+     * @throws NoSuchMethodException     throw when no private constructor is defined.
+     * @throws IllegalAccessException    throw when can not access to the constructor.
+     * @throws InvocationTargetException throw when can not be perform a invocation.
+     * @throws InstantiationException    throw when a instantiation can not be performed.
+     */
+    @Test
+    public void privateConstructorTest() throws NoSuchMethodException, IllegalAccessException,
+            InvocationTargetException, InstantiationException {
+        Constructor<Magnets> constructor = Magnets.class.getDeclaredConstructor();
+        assertTrue(Modifier.isPrivate(constructor.getModifiers()));
+        constructor.setAccessible(true);
+        constructor.newInstance();
+    }
+
+    /**
+     * Basic test for Magnet particles in boxes kata.
+     */
+    @Test
+    public void test1() {
+        System.out.println("Fixed Tests: doubles");
+        assertFuzzyEquals(Magnets.doubles(1, 10), 0.5580321939764581);
+        assertFuzzyEquals(Magnets.doubles(10, 1000), 0.6921486500921933);
+        assertFuzzyEquals(Magnets.doubles(10, 10000), 0.6930471674194457);
+        assertFuzzyEquals(Magnets.doubles(20, 10000), 0.6930471955575918);
+        assertFuzzyEquals(Magnets.doubles(30, 10000), 0.6930471955576123);
+    }
+}