No.163 - LeetCode171

class Solution {
public:
    int titleToNumber(string s) {
        int ans = 0;
        long long base = 1;
        for(int i=s.length()-1;i>=0;i--){
            ans += (s[i] - 'A' + 1)*base;
            base*=26;
        }
        return ans;
    }
};