Added Armstrong number algorithm and tests for it

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

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+package com.williamfiset.algorithms.math;
+
+public class ArmstrongNumber {
+    /*
+     * An Armstrong number is the one where
+     * the sum of each digit of the number to the
+     * power of number of the digits in that number
+     * will be equal to that number for example
+     * 153 (n = 3 digits) is equal to:
+     * 1^3 + 5^3 + 3^3 = 1 + 125 + 27 = 153
+     */
+    public static boolean isArmstrongNumber(int number){
+        int numberLength = (String.valueOf(number)).length();
+        int tracker = number;
+        int answer = 0;
+        while (tracker !=0){
+            int lastDigit = (int) tracker % 10;
+            answer = answer + (int) Math.pow(lastDigit , numberLength);
+            tracker = Math.floorDiv(tracker , 10);
+        }
+        return (answer == number);
+    }
+}

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

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+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/ArmstrongNumberTest.java

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+package com.williamfiset.algorithms.math;
+
+import static com.williamfiset.algorithms.math.ArmstrongNumber.isArmstrongNumber;
+import static org.junit.jupiter.api.Assertions.*;
+import org.junit.*;
+
+
+public class ArmstrongNumberTest {
+    @Test
+    public void armstrongNumberTest(){
+        assertTrue(isArmstrongNumber(1)==true);
+        assertTrue(isArmstrongNumber(153)==true);
+        assertTrue(isArmstrongNumber(1634)==true);
+        assertTrue(isArmstrongNumber(371)==true);
+        assertFalse(isArmstrongNumber(10)==true);
+        assertFalse(isArmstrongNumber(100)==true);
+        assertFalse(isArmstrongNumber(1000)==true);
+    }
+}

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

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+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);
+    }
+}