Multiply Strings

class Solution {
public:
    string multiply(string num1, string num2) {
        if(num1.empty() or num2.empty()) return "0";
        int len1 = num1.size(), len2 = num2.size();
        string ans(len1+len2, '0');
        for(int i = len1 - 1; i >= 0; i--)
        {
            for(int j = len2 - 1; j >= 0; j--)
            {
                int x = num1[i]-'0';
                int y = num2[j]-'0';
                int mult = x*y;
                int ind1 = i+j;
                int ind2 = i+j+1;
                mult += ans[ind2] - '0';
                ans[ind1] += mult/10;
                ans[ind2] = mult%10 + '0';
            }
        }
        int i;
        for( i = 0; i < len1+len2; i++)
        {
            if(ans[i] != '0') break;
        }
        if(i==len1+len2) i--;
        if(i!=0)
            ans.erase(0, i);
        return ans;
    }
};