public int base26ToNumber(String str) {
        int result = 0;
        int pow = 1;
        for(int i = str.length() - 1; i>=0; i--) {
            char s = str.charAt(i);
            s = (char)(s - 'A'+1);
            result += s*pow;
            pow *= 26;
        }
        return result;
    }
Given a positive integer, return its corresponding column title as appear in an Excel sheet.
https://leetcode.com/problems/excel-sheet-column-title/
src/com/interview/misc/ConvertNumberIntoBase26.java