multiply-strings

class Solution {
public:
    string multiply(string num1, string num2) {
        int len=num1.length()+num2.length();
        vector<int>res(len,0);
        for(int i=num1.length()-1;i>=0;i--)
        {
            for(int j=num2.length()-1;j>=0;j--)
            {
                res[i+j+1]+=(num1[i]-'0')*(num2[j]-'0');
            }
        }
        int carry=0;
        for(int i=len-1;i>=0;i--)
            carry+=res[i],res[i]=carry%10,carry/=10;
        while(res[0]==0&&res.size()>1)res.erase(res.begin());
        string ans="";
        for(int i=0;i<res.size();i++)ans+=(res[i]+'0');
        return ans;
    }
};