```
//The idea is simple, just think of the string as a 26 base representation of numbers. Then we have the equation: (Result)_decimal = a_n * 26^(n-1) + a_(n-1) * 26^(n-2) + ... + a0 * 26^0;
class Solution {
public:
int titleToNumber(string s) {
int res = 0;
for(int i=0; i<s.length(); i++){
int exp = s[i] - 'A' + 1;
res = exp * pow(26, s.length() - i -1) + res;
}
return res;
}
};
```