537. Complex Number Multiplication

/*
 Given two strings representing two complex numbers.

You need to return a string representing their multiplication. Note i2 = -1 according to the definition.

Example 1:

Input: "1+1i", "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: "1+-1i", "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.

Note:

    The input strings will not have extra blank.
    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.

*/
//先把字符串从+号分隔开，然后去除字符i，之后加起来就行了
class Solution {
    public String complexNumberMultiply(String a, String b) {
        String[] num1 = a.split("\\+");
        String[] num2 = b.split("\\+");
        String num =null;
        num1[1] = num1[1].replaceAll("i", "");
        num2[1] = num2[1].replaceAll("i", "");
        int a1 = Integer.valueOf(num1[0])*Integer.valueOf(num2[0]);
        int a2 = Integer.valueOf(num1[1])*Integer.valueOf(num2[0]);
        int a3 = Integer.valueOf(num1[0])*Integer.valueOf(num2[1]);
        int a4 = Integer.valueOf(num1[1])*Integer.valueOf(num2[1]);
        return String.valueOf(a1-a4)+"+"+String.valueOf(a3+a2)+"i";
    }
}