leetcode 171 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 

Credits:
Special thanks to @ts for adding this problem and creating all test cases.

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class Solution {
public:
	int titleToNumber(string s) {
		int res = 0;

		for(int i=0; i < s.length(); i++) {
			res = 26*res + (s[i]-'A'+1);
		}
		return res;
	}
}