LeetCode -- Excel Sheet Column Number

题目描述：

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 

本题可以转化为进制转换问题。

思路：和2进制转10进制有点类似，对于AAA，可以理解为26进制的转换：1*26 + 1*26^2 + 1*26^3

实现代码：

public class Solution {
public int TitleToNumber(string s)
{
var sum = 0;
for(var i = s.Length - 1; i >= 0; i--){
var d = s.Length - i;
var n = Num(s[i]);
sum += (int)Math.Pow(26, d-1) * n;
}
return sum;
}

private int Num(char c)
{
return (int)c - 64;
}

}