leetcode 43. Multiply Strings

Given two non-negative integers num1 and num2 represented as strings, return the product of num1 and num2.




class Solution {
public:
    string multiply(string num1, string num2) {
        string s;
        int maxnum = 222;
        int result[maxnum] = {0};
        bool flag = true;
        for(int i = 0; i < num1.length(); i++) {
            for(int j = 0; j < num2.length(); j++) {
                result[i + j] += (num1[num1.length() - 1 - i] - '0') * (num2[num2.length() - 1 -j] - '0') % 10;
                result[i + j + 1] += (num1[num1.length() - 1 - i] - '0') * (num2[num2.length() - 1 -j] - '0') / 10;
                if(result[i + j] >= 10) {
                    result[i + j + 1] += 1;
                    result[i + j] -= 10;
                }
                if(result[i + j + 1] >= 10) {
                    result[i + j + 2] += 1;
                    result[i + j + 1] -= 10;
                }
            }
        }
        for(int i = maxnum - 1; i >= 0; i--) {
            if(flag && result[i] == 0) {
                continue;
            }
            flag = false;

            s += to_string(result[i]);

        }
        if(flag) s = '0';

        return s;

    }
};