171. Excel Sheet Column Number

/*
171. Excel Sheet Column Number
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
    */


public class Solution {
    public int titleToNumber(String s) {
    int len = s.length();
    int[] number = new int[len];
    int titleNumber = 0;
    for(int i = 0; i < len; i++){
    number[i] = (int)(s.charAt(i) - 'A' + 1);
    titleNumber = titleNumber + number[i] * (int)(Math.pow(26, len - i - 1));
    }    
    return titleNumber;      
    }
}

/* a string problem, change string into int, combine with bit operate.*/