leetcode: Excel Sheet Column Number

Related to question Excel Sheet Column Title

Given a column title as appear in an Excel sheet, return its corresponding column number.

For example:

    A -> 1
    B -> 2
    C -> 3
    ...
    Z -> 26
    AA -> 27
    AB -> 28 

class Solution {
public:
    int titleToNumber(string s) {
        int colNum = 0;
		for(int i = 0; i < s.length(); i++)
			colNum = colNum * 26 + (s[i] - '@');
		return colNum;
    }
};