fix: handle negative inputs

Author: vil02

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

@@ -16,6 +16,9 @@ public static void main(String[] args) {
     }
 
     public static int genericRoot(int n) {
+        if (n < 0) {
+            return genericRoot(-n);
+        }
         int root = 0;
         while (n > 0 || root > 9) {
             if (n == 0) {

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

@@ -7,11 +7,18 @@
 import org.junit.jupiter.api.Test;
 
 public class GenericRootTest {
+    private final Map<Integer, Integer> testCases = Map.ofEntries(entry(0, 0), entry(1, 1), entry(12345, 6), entry(123, 6), entry(15937, 7), entry(222222, 3), entry(99999, 9));
     @Test
     public void testGenericRoot() {
-        final Map<Integer, Integer> testCases = Map.ofEntries(entry(0, 0), entry(1, 1), entry(12345, 6), entry(123, 6), entry(15937, 7), entry(222222, 3), entry(99999, 9));
         for (final var tc : testCases.entrySet()) {
             assertEquals(tc.getValue(), GenericRoot.genericRoot(tc.getKey()));
         }
     }
-}
+
+    @Test
+    public void testGenericRootWithNegativeInputs() {
+        for (final var tc : testCases.entrySet()) {
+            assertEquals(tc.getValue(), GenericRoot.genericRoot(-tc.getKey()));
+        }
+    }
+}