[Leetcode] NO. 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 

[题目解析] 该题目比较简单，可以理解为一个26进制的数用10进制数表示的过程。

    public int titleToNumber(String s) {
       if(null == s || s.length() == 0) return -1;
       char sarr[] = s.toCharArray();
       int base = 26;
       int index = sarr.length - 1;
       int result = 0;
       for(char c : sarr){
           int num = c - 'A' + 1;
           result += num * Math.pow(base, index);
           index--;
       }
       return result;  
    }