Check if Word Equals Summation of Two Words

给三个字符串, 问前两个的值转换成数字是否加起来等于第三个.

class Solution {
public:
    bool isSumEqual(string f, string s, string t) {
        return convert(f) + convert(s) == convert(t);
    }
    int convert(string s) {
        int base = 1;
        int res = 0;
        for(int i = s.length() - 1; i >= 0; i--){
            res += base * (s[i] - 'a');
            base *= 10;
        }
        return res;
    }
};