leetcode415 大数相加

    string addStrings(string num1, string num2) {
        int n = num1.size(), m = num2.size();

        // 补齐
        if(n < m)
            for(int i = n;i < m;i++)  num1 = '0' + num1;
        else
            for(int i = m;i < n;i++)  num2 = '0' + num2;

        cout << num1 << " " << num2 << endl;
        int carry = 0;
        string res = "";
        for(int i = max(n,m)-1;i >= 0;i--)
        {
            int tmp = (num1[i]-'0') + (num2[i]-'0') + carry;
            res = to_string(tmp%10) + res;
            carry = tmp/10;
        }
        if(carry != 0)  res = to_string(carry) + res;
        return res;
    }