public class Solution
extends Object
537 - Complex Number Multiplication\.
Medium
A [complex number](https://en.wikipedia.org/wiki/Complex_number) can be represented as a string on the form `"**real**+**imaginary**i"` where:
* `real` is the real part and is an integer in the range `[-100, 100]`.
* `imaginary` is the imaginary part and is an integer in the range `[-100, 100]`.
* i2 == -1.
Given two complex numbers `num1` and `num2` as strings, return _a string of the complex number that represents their multiplications_.
**Example 1:**
**Input:** num1 = "1+1i", num2 = "1+1i"
**Output:** "0+2i"
**Explanation:** (1 + i) \* (1 + i) = 1 + i2 + 2 \* i = 2i, and you need convert it to the form of 0+2i.
**Example 2:**
**Input:** num1 = "1+-1i", num2 = "1+-1i"
**Output:** "0+-2i"
**Explanation:** (1 - i) \* (1 - i) = 1 + i2 - 2 \* i = -2i, and you need convert it to the form of 0+-2i.
**Constraints:**
* `num1` and `num2` are valid complex numbers.