williamfiset#338 added standard deviation and tests for it

src/main/java/com/williamfiset/algorithms/math/StandardDeviation.java

@@ -0,0 +1,17 @@
+package com.williamfiset.algorithms.math;
+
+public class StandardDeviation {
+
+    public static double SD(double arr[]) {
+        double sum = 0, StandardDeviation = 0;
+        int length = arr.length;
+        for (double num : arr) {
+            sum += num;
+        }
+        double mean = sum / length;
+        for (double num : arr) {
+            StandardDeviation = StandardDeviation + Math.pow(num - mean, 2);
+        }
+        return Math.sqrt((StandardDeviation / length));
+    }
+}

src/test/java/com/williamfiset/algorithms/math/StandardDeviationTest.java

@@ -0,0 +1,19 @@
+package com.williamfiset.algorithms.math;
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import org.junit.Test;
+public class StandardDeviationTest {
+
+    @Test
+    public void StandardDeviation4(){
+        double[] array = {-1, -2, -3, -4, -5};
+        double result = StandardDeviation.SD(array);
+        assertEquals(1.4142135623730951, result);
+    }
+
+    @Test
+    public void StandardDeviation2(){
+        double[] array = {3, 5, 7, 20, 55, 12, 1, 3, 5, 4};
+        double result = StandardDeviation.SD(array);
+        assertEquals(15.428869044748549, result);
+    }
+}