Fix: Implement RemoveStars and ComplexMultiply as per guidelines

Author: KhushiAgarwal0406

src/main/java/com/thealgorithms/strings/ComplexMultiply.java

@@ -0,0 +1,26 @@
+package com.thealgorithms.strings;
+
+/**
+ * Multiplies two complex numbers given as strings in "a+bi" format.
+ * Parses the strings manually, performs multiplication, and returns the product.
+ */
+public class ComplexMultiply {
+
+    public static String complexNumberMultiply(String num1, String num2) {
+        // Extract real and imaginary parts without using parseInt
+        int plusIndex1 = num1.indexOf('+');
+        int real1 = Integer.valueOf(num1.substring(0, plusIndex1));
+        int imag1 = Integer.valueOf(num1.substring(plusIndex1 + 1, num1.length() - 1));
+
+        int plusIndex2 = num2.indexOf('+');
+        int real2 = Integer.valueOf(num2.substring(0, plusIndex2));
+        int imag2 = Integer.valueOf(num2.substring(plusIndex2 + 1, num2.length() - 1));
+
+        // Multiply using complex number formula:
+        // (a+bi)(c+di) = (ac - bd) + (ad + bc)i
+        int real = real1 * real2 - imag1 * imag2;
+        int imaginary = real1 * imag2 + imag1 * real2;
+
+        return real + "+" + imaginary + "i";
+    }
+}

src/main/java/com/thealgorithms/strings/ComplexNumber.java

@@ -0,0 +1,29 @@
+package com.thealgorithms.strings;
+
+/**
+ * Removes stars from the input string by deleting the closest non-star character
+ * to the left of each star along with the star itself.
+ *
+ * @param s1 The input string containing stars (*)
+ * @return The string after all stars and their closest left characters are removed
+ */
+public class RemoveStars {
+
+    public static String removeStars(String s1) {
+        StringBuilder sc = new StringBuilder();
+
+        for (int i = 0; i < s1.length(); i++) {
+            char ch = s1.charAt(i);
+
+            if (ch == '*') {
+                if (sc.length() > 0) {
+                    sc.deleteCharAt(sc.length() - 1);
+                }
+            } else {
+                sc.append(ch);
+            }
+        }
+
+        return sc.toString();
+    }
+}