Move ComplexNumberMultiply to maths package and add input validation with tests

Author: SYEDMDSAAD

…ithms/strings/ComplexNumberMultiply.java …orithms/maths/ComplexNumberMultiply.javasrc/main/java/com/thealgorithms/strings/ComplexNumberMultiply.java renamed to src/main/java/com/thealgorithms/maths/ComplexNumberMultiply.java src/main/java/com/thealgorithms/strings/ComplexNumberMultiply.java renamed to src/main/java/com/thealgorithms/maths/ComplexNumberMultiply.java

@@ -1,18 +1,19 @@
-package com.thealgorithms.strings;
+package com.thealgorithms.maths;
 
 /**
  * Multiplies two complex numbers represented as strings in the form "a+bi".
- *
- * Example:
- * Input: 1+1i , 1+1i
- * Output: 0+2i
+ * Supports negative values and validates input format.
  */
 public final class ComplexNumberMultiply {
 
     private ComplexNumberMultiply() {
     }
 
     private static int[] parse(String num) {
+        if (num == null || !num.matches("-?\\d+\\+-?\\d+i")) {
+            throw new IllegalArgumentException("Invalid complex number format: " + num);
+        }
+
         String[] parts = num.split("\\+");
         int real = Integer.parseInt(parts[0]);
         int imaginary = Integer.parseInt(parts[1].replace("i", ""));

…s/strings/ComplexNumberMultiplyTest.java …hms/maths/ComplexNumberMultiplyTest.javasrc/test/java/com/thealgorithms/strings/ComplexNumberMultiplyTest.java renamed to src/test/java/com/thealgorithms/maths/ComplexNumberMultiplyTest.java src/test/java/com/thealgorithms/strings/ComplexNumberMultiplyTest.java renamed to src/test/java/com/thealgorithms/maths/ComplexNumberMultiplyTest.java

@@ -1,6 +1,7 @@
-package com.thealgorithms.strings;
+package com.thealgorithms.maths;
 
 import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertThrows;
 
 import org.junit.jupiter.api.Test;
 
@@ -20,4 +21,16 @@ void testNegative() {
     void testZero() {
         assertEquals("0+0i", ComplexNumberMultiply.multiply("0+0i", "5+3i"));
     }
+
+    @Test
+    void testInvalidFormat() {
+        assertThrows(IllegalArgumentException.class,
+            () -> ComplexNumberMultiply.multiply("1+1", "1+1i"));
+    }
+
+    @Test
+    void testNullInput() {
+        assertThrows(IllegalArgumentException.class,
+            () -> ComplexNumberMultiply.multiply(null, "1+1i"));
+    }
 }