171. Excel Sheet Column Number (Math)

class Solution {
public:
    int titleToNumber(string s) {
        //the last bit of s, multiply 26
        //then left move 1 bit, multiply 26^2
        //iterate
        
        int len = s.length();
        int ret = 0;
        int multiplier = 1;
        int cur;
        for(int i = len-1; i >= 0; i--){
            cur = s[i]-‘A‘+1;
            ret += cur*multiplier;
            multiplier *= 26;
            
        }
        
        return ret;
        
    }
};