[Leetcode]Excel Sheet Column Number

LC Link 1. Line 11, make sure they are all upper case cuz that's our assumption that we will process upper case
2. Line 12, whenever deal with problem to convert bla bla to another number. just use same template
    res = res * (10 or 8 or 26 or whatever) + value on current digit value
    You don't need to consider most right digit value cuz res equals zero at very beginning