Excel Sheet Column Number 把大写字符串转换为整数

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.

只要把数学上的搞清楚，特别简单，主要是用了pow函数，还有就是s.charAt()的使用

public static double pow(double a, double b) {
        return StrictMath.pow(a, b);
    }

Returns the value of the first argument raised to the power of the second argument.

public class Solution {
    public int titleToNumber(String s) {
        int n=s.length();
        int res=0;
        for(int i=0;i<n;i++){
            res+=Math.pow(26,(n-1-i))*(s.charAt(i)-'A'+1);
        }
        return res;
    }
}