171_Excel Sheet Column Number

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 


看成26进制，AA则为 1 * 26 + 1 * 1
　　　　　　BB则为 2 * 26 + 2 * 1

C#代码：

public class Solution {
    public int TitleToNumber(string s) {
        char[] ch = s.ToCharArray();
        int result = 0;
        int pro = 1;//每多一位，则是可以看成26进制
        for(int i = ch.Count() - 1; i >= 0; i--)
        {
            if(i == ch.Count() - 1)
            {
                result += (int)ch[i] - 'A' + 1;
            }
            else
            {
                result += pro * ((int)ch[i] - 'A' + 1);
            }
            pro *= 26;
        }
        return result;
    }
}