171. Excel Sheet Column Number

class Solution {            //second approach, saves memory
public:
    int titleToNumber(string columnTitle) {
        int len=columnTitle.length(),sum=0;        
        for(int i=0;i<len;i++)
            sum+=(columnTitle[i]-64) * pow(26,(len-1)-i); //-64 is used to get 1 for 'A', 2 for 'B'..etc
        return sum;
    }
};
/*Runtime: 0 ms, faster than 100.00% of C++ online submissions for Excel Sheet Column Number.
Memory Usage: 6.1 MB, less than 28.55% of C++ online submissions for Excel Sheet Column Number.*/



// class Solution {             //first approach, used map
// public:
//     int titleToNumber(string columnTitle) {
//         int len=columnTitle.length(),sum=0;
//         map<char,int> m={{'A',1},{'B',2},{'C',3},{'D',4},{'E',5},{'F',6},{'G',7},{'H',8},
//                          {'I',9},{'J',10},{'K',11},{'L',12},{'M',13},{'N',14},{'O',15},{'P',16},
//                          {'Q',17},{'R',18},{'S',19},{'T',20},{'U',21},{'V',22},{'W',23},{'X',24},                                
//                          {'Y',25},{'Z',26}};

//         for(int i=0;i<len;i++)
//             sum+=m[columnTitle[i]] * pow(26,(len-1)-i);
        
//         return sum;
//     }
// };
/*8 ms, 8.3 MB*/