[leetcode] 171.Excel Sheet Column Number

题目：

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

题意：

把26进制的数转化为十进制。

代码比较简单，如下：

class Solution {
public:
int titleToNumber(string s) {
int len = s.length();
if(len == 0)return 0;
int hex = 1;
int result = 0;
for(int i = len - 1; i >= 0; i--)
{
result += hex *(s[i] - 'A' + 1);
hex *= 26;
}
return result;
}
};