LeetCode

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:

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.

public class Solution {
    public String complexNumberMultiply(String a, String b) {
        if (a == null || b == null)
            return null;
        
        String[] ap = a.split("\+");
        int p1 = Integer.parseInt(ap[0]);
        int k1 = Integer.parseInt(ap[1].substring(0, ap[1].length()-1));
        
        String[] bp = b.split("\+");
        int p2 = Integer.parseInt(bp[0]);
        int k2 = Integer.parseInt(bp[1].substring(0, bp[1].length()-1));
        
        int r1 = p1*p2;
        int ri = p1*k2 + k1*p2;
        int ri2 = -(k1*k2);
        
        int p3 = r1 + ri2;
        int k3 = ri;
        
        return p3+"+"+k3+"i";
        
    }
}