Given two strings representing two complex numbers.

You need to return a string representing their multiplication. Note i^2= -1 according to the definition.

Note:

1. The input strings will not have extra blank.
2. The input strings will be given in the form of a+bi, where the integer a and b will both belong to the range of [-100, 100]. And the output should be also in this form.

class Solution {
    public String complexNumberMultiply(String a, String b) {
        int i1 = a.indexOf('+');
        int i2 = b.indexOf('+');

        int r1 = Integer.parseInt(a.substring(0, i1));
        int r2 = Integer.parseInt(b.substring(0, i2));

        int c1 = Integer.parseInt(a.substring(i1 + 1, a.length() - 1));
        int c2 = Integer.parseInt(b.substring(i2 + 1, b.length() - 1));

        return String.valueOf(r1 * r2 - c1 * c2) + "+" + String.valueOf(r1 * c2 + r2 * c1) + "i";
    }
}