1185. Complex Number Multiplication

Code(Language:C++)

class Solution {
public:
    /**
     * @param a: a string
     * @param b: a string
     * @return: a string representing their multiplication
     */
    string complexNumberMultiply(string &a, string &b) {
        // Write your code here
        int sizeA = a.size();
        int i = 0; 
        while(i < sizeA && a[i] != '+'){
            i++; 
        }
        int ai = stoi(a.substr(0, i)); 
        int aq = stoi(a.substr(i + 1, sizeA - 1 - (i + 1))); 
        int size = b.size();
        i = 0; 
        while(i < size && b[i] != '+'){
            i++; 
        }
        int bi = stoi(b.substr(0, i)); 
        int bq = stoi(b.substr(i + 1, size - 1 - (i + 1))); 
        int newI = ai * bi - aq * bq; 
        int newQ = ai * bq + aq * bi; 
        string res = to_string(newI) + "+";
        res += to_string(newQ) + "i";
        return res; 
        
    }
};